As far as his parishioners knew, the Rev. Jay Mullin was on "sick leave" and would be absent from his Plainville, Mass., pulpit until he felt better.

In truth, he had crossed over into a secretive world of church-financed psychiatry.

He flew south in 1992 to a clinic outside Washington, D.C., where a doctor flashed images of children in sexual positions to measure his arousal.

Accused of molesting a boy 22 years earlier, he had been ordered by Cardinal Bernard Law to spend several days at the St. Luke Institute, a Roman Catholic psychiatric hospital in Maryland. He checked in, looked around at the priests from around the country -- some who, like him, had been accused of sexual misconduct -- and gradually realized how deep the problem ran.

"I wasn't aware there was any place like that," recalled Mullin, who denies the abuse charge. "Seeing all of it, I thought, the bishops know where they're sending all of us. They know the magnitude of the problem."

Decades before the case of defrocked Massachusetts priest John Geoghan elevated clergy sexual abuse into a national crisis, the Catholic Church was spending millions of dollars to quietly treat accused sex offenders in a constellation of psychiatric hospitals -- some independent, some church-affiliated -- advertised in the back pages of religious publications.

The facilities frequently used were the St. Luke Institute in Maryland; the Servants of the Paraclete centers in Jemez Springs, N.M., and St. Louis; the Institute of Living in Hartford, Conn., which featured a special clergy program; and the Southdown Institute in Canada.

Since the 1970s, psychiatrists at these facilities have treated accused priests with one-on-one therapy, feminizing hormones and sex-addiction support groups. They sent their reports to bishops, estimating the risk of remission, then released the priests.

Such treatment is typically paid for by the diocese and has cost the church at least $50 million over the past 25 years, estimated Richard Sipe, a psychologist and former priest who treated clergy for 40 years.

A few, like Geoghan, were treated again and again, at numerous centers, and each time slid back into their predatory behavior. Victims, especially those who were molested after the priest had completed treatment, are beginning to wonder what was happening inside the costly psychiatric centers.

"No institution can police itself," said David Clohessy, national director of the Survivors Network for those Abused by Priests. "If chemical companies said, `Just trust us -- send us your dioxins; we'll clean them up,' the public would be wary."

The centers denied repeated requests by the Boston Globe for visits, citing privacy rules.

The treatment centers had been born in a rush of Christian compassion.

On a blustery night during the depths of the Depression, the Rev. Gerald Fitzgerald heard a knock on the back door of his rectory in Brighton and gave food and a coat to a beggar who, as he walked into the dark, turned around and said he, too, was once a priest.

That was the genesis of the Brothers of the Paraclete, a religious order whose mission was to care for troubled priests. In 1947, in New Mexico, Fitzgerald opened a retreat for troubled or alcohol-abusing priests.

Sexual misconduct was not part of the mission then.

When Fitzgerald was asked about treating child molesters, he recommended buying a small Caribbean island and isolating them there, said the Rev. Peter Lechner, the current servant general of the Brothers of the Paraclete.

By the mid-1960s, though, the Paraclete retreat began welcoming an increasing number of pedophiles and, more commonly, ephebophiles, or adults who are sexually aroused by pubescents, Lechner said.

Throughout the 1960s, sexual disorders were treated through psychoanalysis. In the 1970s, Jemez Springs began to "approach modern standards," Lechner said, with regular therapy and an in-house psychiatrist.

Of the 2,000 priests who were treated at Jemez Springs from 1947 to 1968, 10 committed criminal acts after leaving, Lechner said. Among the "graduates" from the 1960s and 1970s were men accused of long lists of molestations, such as the Rev. James Porter, Jason Sigler, the Rev. Rudy Kos, the Rev. David Holley, and Andrew Christian Anderson -- some of whom molested children when the Paracletes sent them out on weekends to officiate in local parishes.

In 1994, the Paraclete fathers shut down the sexual disorders treatment center in New Mexico, after they were forced to pay millions of dollars to settle lawsuits against Porter.

In 1981, a new kind of priest set about building a new kind of treatment center. The Rev. Michael Peterson was a psychiatrist before he converted to Catholicism and entered the priesthood.

An experienced substance abuse counselor, he established a private Catholic hospital called the St. Luke Institute. Priests with alcohol troubles checked into a blue-tiled institutional building flanked by two schoolyards in a predominantly African American neighborhood outside Washington, D.C.

By the mid-1980s, they were joined by an increasing number of priests accused of sexual misconduct. As patients such as Geoghan, Kos, the Rev. Gilbert Gauthe and Monsignor Michael Harris moved in next door, neighbors were not informed.

Priests who arrived at St. Luke after allegations of sexual misconduct found themselves hooked up to CAT scans and electro-encephalograms to measure brain waves, working puzzles for aptitude tests, and -- most controversially -- stripped down for a penile plethysmograph, which measures a man's level of arousal based on the circumference of his penis.

Mullin arrived for an evaluation in 1992. He still shudders when he remembers the plethysmograph, and the pleas he made to the Archdiocese of Boston to exempt him from the test. On the ride back to St. Luke Institute, he said, his driver pulled over and got out of the car so he could cry alone, Mullin said.

"They're observing me. They're videotaping it," he told a Globe reporter. "They finish up with kiddie porn, my first introduction to the whole pornographic industry. It was not a joy by any shape."

Some psychiatrists have come to the defense of the church. Lechner, head of the Paraclete Center, and Dr. Donna Markham, president of Southdown Institute, said church leaders have been forthcoming with case histories and compliant with their recommendations.

Others, though, said the church has manipulated psychiatric expertise. Sipe treated clergy at Seton Psychiatric Institute and served on the board of St. Luke Institute for two years.

"Psychiatry and psychotherapy has been misused by the church in this crisis," Sipe said. "Bishops oftentimes did not give the whole story, but kind of dumped the priests there and just let the psychiatrists `puzzle it out themselves.' They kept the transgressions silent under the guise of confessional material."