PHILADELPHIA -- A Roman Catholic monsignor who became the first U.S. church official to be convicted for covering up sex abuse claims against priests was sentenced Tuesday to three to six years in prison by a judge who said he "enabled monsters in clerical garb ... to destroy the souls of children."

Monsignor William Lynn, the former secretary for clergy at the Archdiocese of Philadelphia, handled priest assignments and child sexual assault complaints from 1992 to 2004. He was accused of transferring problem priests in one of the country's largest parishes and keeping complaints out of the public eye.

"You knew full well what was right, Monsignor Lynn, but you chose wrong," Judge M. Teresa Sarmina said.

Lynn was the first U.S. church official convicted for his handling of abuse claims in the sex scandal that has rocked the Catholic church for more than a decade.

A jury convicted the 61-year-old Lynn last month of felony child endangerment for his oversight of now-defrocked priest Edward Avery, who is serving up to five years in prison after pleading guilty to sexually assaulting an altar boy in church.

In 1992, a doctor told Lynn's office that Avery had abused him years earlier. Lynn sent Avery for treatment, but the church-run facility diagnosed him with an alcohol problem, not a sexual disorder. Avery was returned to ministry and sent to live at the parish where the altar boy was assaulted in 1999.

"I did not intend any harm to come to (Avery's victim)," Lynn said. "My best was not good enough to stop that harm."

The scandal has forced changes in the church. The U.S. Conference of Catholic Bishops have spent tens of millions of dollars on background checks for workers, assistance programs for victims and training for children and teachers on identifying abuse. The bishops also have pledged to remove all accused priests from any public church work.

Advocates for abuse victims, however, contend that dioceses have kept some accused clergy on assignment. They pointed to the Lynn case as an example.

Prosecutors who spent a decade investigating sex abuse complaints kept in secret files at the archdiocese argue that Lynn and unindicted co-conspirators in the church hierarchy kept children in danger.

"He locked away in a vault the names of pedophile priests. He locked in a vault the names of men that he knew had abused children. He now will be locked away for a fraction of the time he kept that secret vault," District Attorney Seth Williams said.

The judge said she believed Lynn initially hoped to address the sex abuse problem and perhaps drafted a 1994 list of accused priests for that reason. But when Cardinal Anthony Bevilacqua had the list destroyed, Lynn chose to remain in the job and obey his bishop while children suffered, she said.

Lawyers for Lynn said insisted he did more than anyone at the archdiocese to meet with victims, get pedophile priests into treatment and send recommendations to the cardinal.

"He did the best he could under absolute awful circumstances," lawyer Thomas Bergstrom said after the hearing. "If he wanted to play the game, he wouldn't have met with them at all."

Lynn's lawyers had sought probation for him, arguing that their client shouldn't serve more time than abusers. They have vowed an appeal of the landmark conviction.

Lynn also was acquitted of conspiracy and a second endangerment count involving a co-defendant, the Rev. James Brennan. The jury deadlocked on a 1996 abuse charge against Brennan, and prosecutors said Monday that they would retry him.

"Protecting children has to be first and foremost," said Barbara Blaine, founder of the Survivors Network of those Abused by Priests. "We're extremely grateful that the judge and the prosecutors did not give Monsignor Lynn special treatment because of his priestly status."