The American Bar Association today made a major exception to its strict code of lawyer-client confidentiality by requiring lawyers to disclose a client's perjury during legal proceedings.

The revision to the proposed code of conduct for lawyers was approved by a 2-to-1 margin, after vigorous protests from trial attorneys that it could "ruin" some clients and would breach a "sacred" duty of secrecy.

The action created one of only two exceptions to that duty allowed by the ABA house of delegates here during its continuing debate over the proposed code. The other, to prevent a client from killing or severely injuring someone, was approved Monday.

All other "whistle-blowing" proposals, whether to prevent corporate crimes or private fraud, have been defeated here in a series of stinging rejections of those sponsoring the ethics revision.

Although they approved the perjury provision today, the lawyers refused to require equal candor outside the courtroom in dealings with private parties. Defeating yet another proposed revision, the lawyers forbade disclosure of secrets even when necessary "to avoid assisting a criminal or fraudulent act," short of physical assault, by a client.

The contest over confidentiality has turned into one of the most heated ABA disputes in a decade. It was set off, in part, by the Watergate scandals, in which dozens of lawyers were implicated, giving the legal profession a black eye.

After Monday's votes, proponents of major changes privately expressed fears that what they consider a "reform" effort was beginning to backfire and produce further image problems for the profession. That feeling appeared to influence today's vote.

The change approved today, if adopted by the states, would replace ambiguous provisions in the current code of conduct governing situations, such as criminal trials, where a lawyer discovers a lie by his client.

Under the rule, the lawyer must make sure that the lie is not permitted to stand, either by convincing the client to recant or, if necessary, by revealing the lie to the court.

Any other approach, said Michael Frank, a leader in the fight for the rule, would be "asking a jury to decide that what you know to be a lie is the truth." This association "cannot go on record advocating assisting a client in the advancement of perjured testimony," said Mark Harrison, an Arizona delegate.

Only such impassioned pleas appeared to prevent defeat of the proposed rule. The American College of Trial Lawyers, which helped beat back Monday's more liberal proposals, was joined today by the criminal justice and legal aid sections of the ABA in trying to scuttle this one.

"Can you imagine us going in and destroying a client's position like this?" said Curt W. Melchior of San Francisco. "This could ruin him."

"All of us tell a client to 'tell me everything,' " said Robert F. Hanley of Denver. "He's not going to tell you anything" under the new rule.

Some opponents expressed concern that such disclosures would violate defendants' constitutional rights to a fair trial. Sponsors have said, however, that state and federal court rulings designed to protect those rights would modify bar disciplinary rules where necessary.

The delegates will continue to consider the rules here this week and at a meeting in Atlanta this summer.