WASHINGTON - Resurrecting an impeachment controversy, a federal judge ruled Wednesday that President Clinton ''committed a criminal violation of the Privacy Act'' by releasing personal letters to undermine the credibility of one of his accusers.
Clinton immediately disputed the decision, saying he reluctantly released the letters two years ago because ''it was the only way I knew to refute allegations'' by Kathleen Willey of an unwanted sexual advance.
U.S. District Judge Royce Lamberth concluded the president and three top White House lawyers disregarded an earlier court ruling when they made Willey's letters public in the midst of the Monica Lewinsky scandal in 1998.
''This court cannot accept or condone this unlawful action,'' Lamberth wrote in a decision that clears the way for a lawsuit filed by the conservative group Judicial Watch to delve further into the issue.
Initially, Lamberth's ruling simply requires White House lawyers to answer questions they earlier rejected about the decision to release the letters. But it could open the door for an eventual lawsuit by Willey.
And the Justice Department, which is reviewing the decision, has an open investigation into another impeachment-related release of damaging information about a critic - the Pentagon's release of data from Linda Tripp's personnel file.
Independent Counsel Robert Ray, who must decide whether to indict Clinton after he leaves office, cannot prosecute a Privacy Act case because it only is a misdemeanor.
The White House plans to appeal. Clinton said he never even considered the Privacy Act when he made the decision to release the letters.
The president said he ''decided to do it reluctantly only because it was the only way I knew to refute allegations that were made against me that were untrue.''
He also took a swipe at Lamberth, noting the Republican appointee ''somehow acquired a significant percentage of the cases involving the White House. That's an interesting story.''
White House Counsel Beth Nolan said Lamberth's opinion is inconsistent with ''every Administration'' since 1975, ''Republican and Democratic alike,'' that the White House is not subject to the Privacy Act.
The judge, who has presided over several lawsuits filed against the Clinton administration by Judicial Watch, minced no words, writing: ''The president committed a criminal violation of the Privacy Act.''
The judge said former White House Counsel Charles F.C. Ruff, Deputy Counsel Bruce Lindsey and former Deputy Counsel Cheryl Mills engaged in discussions that led to the release of the letters. And he rejected White House arguments that the lawyers' conversations were protected by attorney-client confidentiality.
He noted the lawyers recommended the president release the letters just nine months after he issued a ruling that the White House needed to follow the Privacy Act.
''The White House and president were aware that they were subject to the Privacy Act, and yet chose to violate its provisions,'' Lamberth wrote.
Presidential aides used the letters to undercut Willey's allegations, saying the correspondence showed the Virginia woman remained friendly with the president after the alleged sexual encounter. Clinton steadfastly has denied making the advance.
Phone calls to Willey and her lawyer in Powhatan, Va., were not returned Wednesday.
Lawrence Barcella, a veteran Washington lawyer, questioned the ruling.
''In Clinton's case, he appears to be relying on the advice of his legal counsel. Differing legal opinions don't always equal a violation,'' Barcella said.
David Sobel, general counsel for the Electronic Privacy Information Center, said Willey may have a strong basis for a lawsuit against the president. ''It is highly unusual if not unprecedented for a court to find a criminal violation of the Privacy Act,'' Sobel said.
Lamberth's ruling comes in a lawsuit by appointees from the Reagan and Bush administrations over the Clinton White House's gathering of hundreds of FBI background files on Republican appointees. The judge gave Judicial Watch, which is representing the former officials, wide latitude in exploring whether the White House routinely gathered and released damaging information about opponents.
Lamberth found that releasing the Willey letters was a violation of the Privacy Act because they had been placed in the files of a federal agency - in this case the White House - and so must remain confidential.
The group was allowed to ask extensive written questions about the Willey letters even though Willey is not party to the suit. Presidential aides refused to answer some questions, prompting Lamberth's ruling.
Willey was a White House volunteer seeking a full-time paying job when she went to Clinton in 1993 because her husband was in deep financial trouble. Willey's husband killed himself later that same day.
In grand jury testimony, Clinton referred to the release of the letters. ''You know what evidence was released after the '60 Minutes' broadcast that I think pretty well shattered Kathleen Willey's credibility,'' he told prosecutors.