The survey, the most complete compilation of data on the problem available, contains the names and histories of 1,205 accused priests. It counted 4,268 people who have claimed publicly or in lawsuits to have been abused by priests, though experts say there are surely many more who have remained silent.

The Rev. Robert J. Silva of the National Federation of Priests Councils says seminarians were once treated "basically as little children." Photo by Peter Thompson for The New York Times.

The survey provides a statistical framework for viewing the sexual abuse crisis against the modern history of the American Catholic Church. It found, for example, that most priests accused of abuse were ordained between the mid-1950's and the 1970's, a period of upheaval in the church, when men trained in the traditional authoritarian seminary system were sent out to serve in a rapidly changing church and social culture.

Most of the abuse occurred in the 1970's and 1980's, the survey found. The number of priests accused of abuse declined sharply by the 1990's.

But the data show that priests secretly violated vulnerable youth long before the first victims sued the church and went public in 1984 in Louisiana. Some offenses date from the 1930's.

"This has been going on for decades, probably centuries," said Richard K. O'Connor, a former Dominican priest who says he was one of 10 boys sexually assaulted by three priests in a South Bronx parish in 1940, when he was 10. "It's just that all of a sudden, they got caught."

The survey also shows how pervasive the abuse has been. Using information from court records, news reports, church documents and interviews, the survey found accusations of abuses in all but 16 of the 177 Latin Rite dioceses in the United States.

Every region was seriously affected, with 206 accused priests in the West, 246 in the South, 335 in the Midwest and 434 in the Northeast. (Some priests were counted more than once if they abused in more than one region.) The crisis reached not only big cities like Boston and Los Angeles but smaller ones like Louisville, Ky., with 27 priests accused, and St. Cloud, Minn., with 9.

The scandal has set off an intense debate within the church over what caused it and what can resolve it. Many Catholic conservatives blame the reforms of the Second Vatican Council and the social upheaval of the 1960's for removing priestly inhibitions on sexuality and dissent. Liberals tend to find the root causes in what they call the church's repressive approach to sex, including priestly celibacy, and its deeply ingrained culture of secrecy. The Times database provides evidence to support the arguments of both sides.

The data, together with extensive interviews with priests and former priests, abuse victims, church historians, psychologists and experts on sexual disorders, suggest that although the problem involved only a small percentage of priests, it was deeply embedded in the culture of the Catholic priesthood. Many priests began seminary training as young as 13, and all of them spent years being groomed in an insular world in which sexual secrets and transgressions were considered a matter for the confessional, not the criminal courts.

The Times survey counted priests from dioceses and religious orders who had been accused by name of sexually abusing one or more children. It determined that 1.8 percent of all priests ordained from 1950 to 2001 had been accused of abuse.

But the research also suggested that the extent of the problem remains hidden. In dioceses that have divulged what they say are complete lists of abusive priests — under court orders or voluntarily — the percentages are far higher. In Baltimore, an estimated 6.2 percent of priests ordained in the last half-century have been implicated in the abuse of minors. In Manchester, N.H., the percentage is 7.7, and in Boston it is 5.3.

In November, Cardinal Joseph Ratzinger, a top Vatican official, declared that "less than 1 percent" of priests had abused minors, and that there were fewer sex offenders among priests than other groups.

But experts say it is impossible to know whether priests abuse more or less often than people in other professions, or even in the general population, because there are no reliable studies.

The Times data include only cases in which priests were named, and many bishops have released only partial lists of accused priests, or refused to identify any.

"My assessment is it's only the tip of the iceberg," said William R. Stayton, professor and coordinator of the human sexuality doctoral program at Widener University in Chester, Pa., who was shown the results of the Times study. "You really don't have a true picture. I have worked with many clergy sexual abuse cases over the years, and very, very few of them were reported."

That attitude may be changing. Since last January, when the Boston Archdiocese was forced to disclose documents showing that for years its officials had protected priests who molested, hundreds of people have come forward with accusations of abuse.

In those 12 months, as the scandal exploded throughout the church, 432 accused priests have resigned, retired or been removed from ministry.

Because in the nearly 20 years since the problem surfaced the American bishops have refused to cooperate with researchers who sought to initiate studies, the Times study offers the fullest picture possible of the extent of sexual abuse within the church. These are among the other findings:

• Half of the priests in the database were accused of molesting more than one minor, and 16 percent are accused of having had five or more victims.

• Eighty percent of the priests were accused of molesting boys. The percentage is nearly the opposite for laypeople accused of abuse; their victims are mostly girls.

• While the majority of the priests were accused of molesting teenagers only, 43 percent were accused of molesting children 12 and younger. Experts in sexual disorders say the likeliest repeat offenders are those who abuse prepubescent children and boys.

• Those ordained in 1970 and 1975 included the highest percentage of priests accused of abuse: 3.3 percent. More known offenders were ordained in the 1970's than in any other decade.

• Of the 432 priests removed from or who left the ministry last year, 183 were suspended, living in limbo while waiting for church panels to decide their cases. Bishops were known to have begun the most drastic step, defrocking, for only 11 priests, despite agreeing to a policy at their Dallas meeting last year that encouraged this option. At least nine priests have been reinstated.

• The Boston Archdiocese, which received the most scrutiny in news reports last year, did have the most accused priests — 94 — but not the worst problem proportionally. More than a dozen other dioceses had a higher rate of accused priests when taken as a percentage of their active priests.

The study shows only what has become public about a crime usually kept secret by both abuser and victim. Some experts, for instance, contend that the sharp drop in priests accused of abuse in the 1990's is less a result of efforts by the church to confront the problem than a reflection that the victims have not yet come forward.

Resisting Only 'Punch and Judy'

The first significant number of priests accused of abuse to emerge in the study were trained in the 1950's and early 1960's. It was the heyday of American Catholicism, when newly comfortable middle-class Catholics financed hundreds of new parochial schools and seminaries, and many of the faith's best and brightest enlisted to serve their church. Many are bishops today.

"The priesthood was riding high," said Jay P. Dolan, a professor of history at the University of Notre Dame and author of "In Search of American Catholicism" (Oxford, 2002). "A lot of boys were entering the seminary. It appealed to your altruism, your desire to help others, and it was a profession very highly valued by Catholics and others."

To qualify, a young man needed little more than to say he felt "called" to a priestly vocation. "Getting in the seminary then was a rather easy process," said Mr. Dolan, who entered a seminary in 1954. "There was no screening of candidates at all. They accepted anybody, and the numbers were incredible."

It was typical then for boys to begin their training in a minor seminary at age 13 or 14, continuing directly through for 10 or 12 years until ordination. Many of the minor seminaries, most of which were phased out starting in the 1970's, were essentially boarding schools. There young men lived together in semi-monastic isolation, missing most of the social, sexual and developmental milestones their peers were experiencing back home.

"If you remained in the system, you were treated the same way when you were 26 as when you were 14 — basically as little children," said the Rev. Robert J. Silva, president of the National Federation of Priests Councils, who studied to be a priest in northern California in the 1950's. "On Thursdays, you signed out to go to town and buy what you needed. You couldn't go to a movie, to a restaurant. You went to a drugstore, and you came home. Once a month when we were younger we used to get what we called a walk into town. We could go and get milkshakes, but we always went together. You rarely socialized with other people."

Seminary instructors warned students to stay away from temptations, but they never mentioned altar boys and teenagers. Their chief concerns, Mr. Dolan remembers, were "Punch and Judy" — alcohol and women.

Diocesan priests take a vow of celibacy, promising never to marry or have sex with women. Seminarians were taught that all other sexual activity was unchaste and sinful, but not a violation of the celibacy vow.

Some priests relied on this distinction to rationalize to their victims, the authorities or church superiors that mutual masturbation, fellatio or touching children's bodies, however wrong, left their celibacy vow intact, according to some victims, therapists who treated the abusers and court records.

In general, though, the entire subject of sexuality was taboo in seminaries.

"It amounted to don't ask, don't tell, don't touch," said Paul E. Dinter, a former priest ordained in 1965 and the author of a new book, "The Other Side of the Altar" (Farrar Straus & Giroux). "In my lifetime there were still seminaries handing out paddles so you could tuck your shirt into your pants and never touch yourself. There were nuns showering in gowns so they were never naked."

Psychologists who have treated priest offenders now say that such a sexually repressed environment appealed to some young men who felt guilty about being sexually stimulated by children, male teenagers or adult men.

Dr. Eli Coleman, professor and director of the Program in Human Sexuality at the University of Minnesota Medical School, said, "The church was definitely an attractive haven for a lot of people who naturally wished that somehow, through a spiritual life, they would not have to deal with those conflicts."

Accused priests first became a significant proportion of ordination classes in 1956, the Times study found. Of that class, 32 priests have been accused of abuse. Of priests ordained from 1956 through 1959, 119, or 1.8 percent, were accused of abuse. The number of those accused out of each ordination class fluctuated only slightly through about 1963, when it reached 40, or 2.6 percent of that year's class. Then it remained fairly consistent through the mid-1970's. But since fewer men were being ordained in the 1970's, priests accused of abuse made up a larger proportion of their classes.

Many of these priests did not commit their offenses until the 1960's or 1970's. But the Times research found that 63 priests were accused of abuse that occurred in the 1950's, and 7 in the decades before.

The relatively low numbers do not indicate that the sexual abuse of children was not a problem in those days, sexual abuse experts said, since it is likely that people of previous generations rarely reported it because of the social stigma, the fear of retribution or the failure to understand that what happened to them was abuse.

Mr. O'Connor, who is now 73, said that when he was raped at age 10 by priests at St. Rita of Cascia Shrine Church in the South Bronx, he did not dare tell anyone. He said his mother found out only when she discovered blood on his underwear. (The New York Archdiocese said it was unable to comment on the allegation because the director of priest personnel was traveling abroad.)

Mr. O'Connor said that his parents wrote a letter complaining to the senior pastor, and even threatened to hire a lawyer. But he said he knew of 10 other boys who had been similarly attacked and whose mothers had learned of the molestations but said nothing. He says the women, devout Catholics, refused to confront the priests.

"In the 40's and 50's, when you were talking to a priest, it was like you were talking to Jesus Christ himself," Mr. O'Connor said.

One day, the three priests disappeared from the South Bronx parish, Mr. O'Connor said. His parents later learned that their letter had eventually made its way to Cardinal Francis Spellman of New York, who sent the three priests, all now dead, to work in parishes upstate.

Loosening the Roman Collar

By the mid-1960's young priests emerged from their near-cloistered seminaries and stood blinking at a world changing around them.

There were simultaneous cultural revolutions inside and outside the church. The Second Vatican Council, which ended in 1965, suddenly lowered barriers between the church and modern society, and between the clergy and laypeople. The liturgy went from Latin to English, the altar was turned around and priests faced the people at Mass for the first time in centuries. Laypeople took on leadership roles. Priests and nuns joined the antiwar movement and the civil rights struggle, rubbing elbows with Protestants and Jews, college students and feminists.

Priests who had had strict curfews in the rectories where they lived with their fellow priests were suddenly free to come and go. They bought cars, were invited to meetings and marches, moved about without their collars.

Father Silva, ordained in 1965 in San Francisco, said: "All of a sudden, father is expected to be close to the folks, and so he takes off his cassock, he takes off the Roman collar and puts on a sport shirt, and he's assigned to work with the teenagers.

"Here you are developmentally somewhere between age 13 and 16, never having ever looked at your own sexuality, never having asked the question, gay or straight? — you didn't even know the words," Father Silva said. "And so you find yourself with the teen club, and father is taking the students on a ski trip overnight. If he is emotionally still a teenager, very inappropriate things can happen."

In fact, it was customary for new priests then to be assigned to supervise the teen club or the altar boys, church experts said. Parishes in those days had full complements of three or more priests, and the priest with the least seniority was often given the job with the least status — working with youngsters.

Dr. Mary Gail Frawley-O'Dea, executive director of the Trauma Treatment Center of the Manhattan Institute for Psychoanalysis and a sexual abuse expert who addressed the Catholic bishops at their Dallas meeting last year, said of priests: "They were thrown into the company of young men who were having adolescences very different than they had — dating, masturbating, having buddies. The priest saw himself as an age mate of the youth, and better yet, as a leader of the pack. At some point, all those genuine human needs for closeness, including touch, just burst."

The Times study found that 4 of 5 victims of priests were male. That is nearly the opposite of those victimized by nonpriests, nearly two-thirds of whom are female, several experts in sexual abuse said.

The experts offered several possible explanations: that priests simply had more unfettered access to boys; that priests who had had their first sexual encounters in seminaries were more likely to be attracted to boys; that a high percentage of priests were gay; that women and girls hesitated to report such abuse for fear they would be accused of inviting the attention.

Over all, 256 priests were reported to have abused minors in the 1960's. There were 537 in the 1970's and 510 in the 1980's, before a drop to 211 in the 1990's. The numbers do not prove that the upheaval in the church and society in the 1960's and 70's caused the abuse, but experts who reviewed The Times's research said it was important to consider the historical context in which the scandal occurred.

The church was jolted by two earthquakes in the 1960's. Vatican II was the first, and Humanae Vitae, the papal encyclical upholding the church's condemnation of artificial birth control in 1968, was the second.

Amid surging use of the birth control pill, many priests say it fell on them to promulgate a teaching they could not agree with. And many said the controversy removed their inhibitions about criticizing or even disregarding church teachings on sexuality.

"People were beginning to decide that the church couldn't make the rules anymore," Mr. Dinter said.

At the same time, many healthier priests were jumping ship. Beginning in 1967 and for the next 10 years, priests abandoned their vocation in droves. About 525 left in 1968, 675 in 1970 and 575 in 1973 — at the height, more than 1 percent of the American priesthood annually, according to figures supplied by the Center for Applied Research in the Apostolate at Georgetown University.

Many left disillusioned that Vatican II had not eased the rigid episcopal hierarchy or the rules on celibacy, and many left to marry. Those left behind included a greater percentage of priests who were theologically conservative, gay or maladjusted, a trend that the bishops had apparently begun to note. In 1971, they commissioned a study by Dr. Eugene Kennedy, a psychologist at Loyola University of America and a former priest, and Dr. Victor Heckler, the principal investigator. Their report, "The American Priest: Psychological Investigations," found that 57 percent of priests were psychologically "underdeveloped."

Sinners in Therapy

By the 1970's and 1980's, when abuse was reaching a peak, church leaders were still doing little to confront it effectively. As they had for centuries, bishops and priests regarded priests who molested not as criminals but merely sinners.

"If a priest was having sex with a boy it meant he was weak and gave in," Mr. Dinter said. "It meant he should go to confession and not be weak again."

Even a serial offender like John J. Geoghan, a defrocked priest who was convicted of abuse last year in Boston, was repeatedly given a pass by his bishops and his peers. He has been accused of molesting more than 130 children over 30 years in a half-dozen parishes.

"If you read his record, seminary rectors were wondering about him," Dr. Kennedy said. "But the culture of the priesthood was very supportive, so a fellow got a lot of cover just for wearing a Roman collar."

By the 1970's, some bishops had begun referring priests to therapists, but most of the therapists were priests, or working at church-related treatment centers, Dr. Frawley-O'Dea said.

Bishops who turned to outside clinicians sometimes disregarded the advice they were given. Dr. Stayton recalls that in the early 1970's, a bishop asked him to have precisely six sessions with a priest who was molesting children.

After the six meetings, Dr. Stayton said: "They transferred him to a high school someplace outside of his diocese, and they didn't ask me. I never had to make a report, I just had to turn in a bill. I would never have recommended that he go to a high school."

The Times study found that half of the priests accused of abuse had more than one victim, and one-third had three or more. In the rest of the cases, only one victim has come to light. But there have been many cases in which an accused priest insisted he had only one victim, and more came forward later. Experts in sexual disorders say that the high percentage of priests with multiple victims suggests that the church was dealing with a cohort of offenders who were not easily stopped.

Dr. David Finkelhor, director of the Crimes Against Children Research Center at the University of New Hampshire, said, "The more victims you have, the higher chance of reoffending."

Sixteen percent of the priests accused of abuse had five or more victims, which may be an indication, said Dr. Finkelhor, that these were "compulsive child molesters — those who actually have a preference for juvenile victims. That's their primary sexual orientation."

By the mid-1980's, the warning had been sounded. The Rev. Gilbert Gauthe, a Louisiana priest who molested as many as 100 boys, was sentenced to 20 years in prison. Two priests and a lawyer who defended the church in that case produced a report predicting that sexual abuse by priests could eventually cost the church in the United States more than $1 billion. The report was never distributed to the bishops.

A Scandal's Unwritten Chapter

The Times's research confirms a point that the nation's Catholic bishops made as the scandal escalated last year: most of the abuse cases are old. Of the accused priests, 211 abused in the 1990's, and 36 since 2000.

The bishops say the abuse declined because they began to address the problem in the mid-1980's. In 1992 the bishops' conference issued five recommendations, which included removing an accused priest from ministry for evaluation and treatment, and reporting cases to law enforcement.

Seminaries were overhauled, in part, in recognition that they were producing unhealthy priests. By the late 1980's, many Catholic seminaries and dioceses began psychological screening of candidates for the priesthood, said Sister Katerina Schuth, a sociologist at St. Paul's Seminary at the University of St. Thomas.

Human sexuality was added to seminary curriculums soon after 1992, when Pope John Paul II called for the church to pay attention to the "human formation" of priests, said Sister Schuth. Studies show that more seminarians and priests now identify themselves as homosexual than in previous generations, and with the openness has come more candid discussion in seminaries of celibacy and chastity, she said.

The decline in priest cases in the 1990's parallels a 40 percent decline in the sexual abuse of children generally, Dr. Finkelhor said. There are many reasons, he said: more offenders are incarcerated for longer periods; children are more closely supervised; and there is more awareness about identifying and reporting sexual abuse.

But many say that the real reason for the decline may be simply that the victims of the 1990's have not surfaced yet.

"You will see some kind of a bubble in 2005, when the people who were abused in the 1990's come forward," said Dr. Frawley-O'Dea, who has treated many abuse victims. "It takes a lot of survivors until their mid-20's, when they have accumulated enough life experience, to know they were messed up."

But there could be another explanation for the 1990's decline: the church is still covering up cases. Despite the pressure on bishops over the last year to reveal the extent of the abuse, some refused to release the number of accusations or the names of the accused priests.

Anthony Zirilli and the research staff of The New York Times contributed to this report.