The American Bar Association, after six years of one of the most intense debates in its history, today gave final approval to a new model code of ethics for lawyers that preserves most of the traditional prohibitions on disclosure of client confidences.

Watergate-spurred efforts to alter the code radically by incorporating whistle-blowing requirements on lawyers who observe their clients engaged in fraud were defeated last year.

In a compromise approved today, however, the association's 380-member House of Delegates did bend slightly the principle of lawyer-client confidentiality by giving lawyers the right to alert potential victims to ongoing fraud or wrongdoing by clients, after withdrawing from representing them.

The new rules and accompanying interpretations have no force unless adopted by individual states and the federal judiciary, which are free to accept or reject all or part of them. Considerable controversy is expected as the debate shifts to the state level, with the bar associations of New York, California and Florida already on record in opposition for different reasons.

The new "model rules of professional conduct" cover virtually all aspects of the practice of law, from discussion of fees with clients to the type of letterheads law firms may use to restrictions on lawyer advertising.

But most of the controversy centers on proposals to change the behavior of lawyers when confronted with fraudulent behavior by clients.

It was the first major revision of the ethics code in 14 years. During that time, the legal profession underwent a public image crisis when lawyers were heavily involved in the Watergate scandal.

The revisions consist of a series of short and specific rules, accompanied by lengthier "comments" which are used to help interpret the rules. The rules were approved last winter in New Orleans by the ABA. Today the association approved the comments and the code in their entirety.

In New Orleans, the lawyers refused virtually all proposed exceptions to confidentiality, defeating a proposed rule which would have allowed them to disclose an ongoing fraud by a client.

Today, in the less important comment section, they gave attorneys one new route to follow in such situations: After failing to stop a client's wrongdoing and withdrawing from a case or client, an attorney may disavow any legal documents or papers he previously prepared for the client, and may give notice of that revocation to people affected by the potential fraud.

A lawyer who discovers, for example, that he unwittingly helped prepare a fraudulent loan application may withdraw it and notify the lender.

Many of the new provisions simply clarify or elaborate on previous rules, but Prof. Geoffrey Hazard of Yale Law School said there were "important" advances in some areas.

The new rules say that a lawyer should explain fee rates to a new client, preferably in advance and in writing. They also specify explanations in "contingent fee agreements" of what percentage a lawyer might get of a court award to a client in a suit.

"In a new client-lawyer relationship," the accompanying comment said, "an understanding as to the fee should be promptly established."

The new rules define and specifically prohibit a variety of situations in which one lawyer or law firm may be representing various clients whose interests conflict.

Another provision involving confidentiality in civil court cases requires lawyers in some circumstances to disclose perjury when they discover it.

The comments said it was debatable whether such disclosures could be made in criminal trials because of questions about whether that would violate constitutional rights of defendants against self-incrimination.

The rules set out specific guidelines for lawyers representing organizations, for lawyers who go from government to private employment and for lawyer advertising.

The rules were approved by a voice vote which reflected a sizable minority in opposition. Florida bar officials said they thought disclosure had not gone far enough. California bar leaders said it went too far.