WASHINGTON -- Former Oklahoma Gov. Frank Keating resigned June 16 as chairman of the National Review Board formed by the U.S. bishops last year to monitor their performance on combating sexual abuse of minors by clergy.

The move followed a heated controversy with Los Angeles Cardinal Roger M. Mahony over Keating's characterization of some bishops as being as secretive as a crime family. But in his resignation letter Keating said he has been talking for the past two months about resigning this June after one full year in the job.

In the letter, however, Keating also defended his recent remarks.

"As I have recently said, and have repeated on several occasions, our church is a faith institution. A home to Christ's people. It is not a criminal enterprise," he wrote.

"It does not condone and cover up criminal activity. It does not follow a code of silence," he added. "My remarks, which some bishops found offensive, were deadly accurate. I make no apology. To resist grand jury subpoenas, to suppress the names of offending clerics, to deny, to obfuscate, to explain away: that is the model of a criminal organization, not my church."

He called the sex abuse scandal "a poisonous aberration, a black page in our history that cannot ever recur."

Bishop Wilton D. Gregory of Belleville, Ill., president of the U.S. Conference of Catholic Bishops, said Keating has made an "enormous contribution" to the church in his year as head of the review board.

In a letter accepting Keating's resignation Bishop Gregory wrote, "I will always be grateful to you for your immediate and generous willingness to contribute to this unprecedented endeavor."

"Because the task you took on was unprecedented and had to be carried out in an intense environment which gives rise to strong emotions under the close observation of the media, there were bound to be moments of difficulty," the bishop added.

Bishop Gregory named Keating to head the National Review Board last June in Dallas, immediately after the nation's bishops adopted the "Charter for the Protection of Children and Young People" which established the board.

Keating was then nearing the end of his second term as governor of Oklahoma and, under that state's term limits, was ineligible for re-election. In January he moved to Washington as head of the American Council of Life Insurers.

Justice Anne M. Burke of the Illinois Appellate Court in Chicago, vice chairwoman of the board, was expected to lead the board until a successor to Keating is named.

The 13-member National Review Board is charged with monitoring the U.S. bishops' compliance with the child protection charter, conducting annual audits in every diocese, and providing yearly reports on the results to the USCCB president, who is to publish those reports.

The charter also gave the board responsibility for two major research projects -- one on the extent of the problem of clergy sexual abuse of minors in the U.S. church and another on the "causes and context" of the crisis.

In his resignation letter Keating said the board, with Bishop Gregory's support, has "accomplished much."

"We have begun the causes and context, scope and audit processes," he said. "The audit is the most significant. Never again will any bishop be able to hide and avoid the scandal of sex abuse in his diocese. As a former FBI agent and U.S. attorney, I am convinced that pouring law enforcement and audit resources annually into each diocese will reclaim Catholic lay confidence. All of us can be assured of zero tolerance, transparency and criminal referral because outsiders will make sure that is the case."

"Our message was clear," he added. "Sex abuse is not just a moral lapse. It is a crime that should be fully prosecuted."

Just days before he resigned, Keating said in an interview with the Los Angeles Times that some unnamed bishops have been acting like the Cosa Nostra, the secretive U.S. branch of the Mafia, in their efforts to hide and suppress information about clergy sexual abuse. He also criticized some bishops, citing Cardinal Mahony by name, for what he characterized as resistance to a national survey on the extent of the problem being conducted by the John Jay College of Criminal Justice in New York.

Cardinal Mahony called Keating's comparison of bishops to La Cosa Nostra "off the wall." He strongly defended the position he and the other California bishops had taken on the John Jay study, calling for changes in the researchers' survey protocols to permit the bishops to respond to the questions without violating California confidentiality laws.

The day before the Keating interview was reported in the Times, the researchers made changes in their survey protocols that satisfied the California bishops, and Cardinal Mahony and the other bishops of the state said they could now participate in the study without breaking the law.