When the Federal Bureau of Investigation questions the credibility of the attorney general, things get nasty. In the Watergate scandal in the 1970s, the FBI helped prosecute the crimes and cover-up. Attorney General John N. Mitchell was found guilty of conspiracy, obstruction of justice and perjury and spent 19 months in prison.

Now the present FBI director, Robert S. Mueller III, has publicly contradicted recent testimony by Attorney General Alberto R. Gonzales about a bitter internal dispute three years ago over the Bush administration’s secret warrantless wiretapping operation.

Earlier this month, Mr. Mueller turned over to the House Judiciary committee his notes about Mr. Gonzales’s late-night visit to the hospital room of then Attorney General John Ashcroft to try to persuade Mr. Ashcroft to approve a renewal of the controversial warrantless eavesdropping program.

Mr. Gonzales, then the White House counsel, testified last month that Mr. Ashcroft, who was in intensive care recovering from gallstone surgery, was “lucid” and “did most of the talking.”

Mr. Mueller reached the hospital a few minutes after Mr. Gonzales’ departure and found Mr. Ashcroft “feeble, barely articulate, clearly stressed.” The Mueller notes also confirmed an account of the meeting by James B. Comey, then deputy attorney general, who said Mr. Ashcroft had told Mr. Gonzales that he was not well enough to make decisions in the hospital.

Mr. Comey, as acting attorney general, had told the White House a few days earlier that Justice Department lawyers had found parts of the eavesdropping program unconstitutional.

Mr. Ashcroft’s wife, Janet, learned that Mr. Gonzales and White House chief of staff Andrew H. Card Jr. were on their way to the hospital and summoned Mr. Comey to keep them from pressuring her husband. Mr. Mueller said Mr. Comey asked him to appraise Mr. Ashcroft’s condition and order that no visitors, other than family, be allowed to see the attorney general without Mr. Comey’s consent.

The heavily edited Mueller notes provide new insight into the secret legal dispute in 2004. They list 26 meetings and phone calls in the three weeks before and after the bedside encounter, but details of the conversations are blacked out. Mr. Mueller, Mr. Ashcroft, Mr. Comey and many other senior officials of the Justice Department and FBI had threatened to resign over the issue. They relented only when President Bush ordered yet-unspecified changes in the program.

Mr. Mueller’s flat assertions that directly contradict those of Mr. Gonzales are significant and unusual because Mr. Gonzales is, in effect, Mr. Mueller’s boss. The FBI is an agency of the Justice Department, but it has something of an independent role and pledges as the first of its core values “Rigorous obedience to the Constitution of the United States.” Its director is appointed by the president for a term not to exceed 10 years.

As the shadowy dispute unfolds, we need to know what were the constitutional objections, how were they resolved, how extensive is current eavesdropping.

More immediately, what is Mr. Gonzales’ future, with his credibility in tatters and impeachment a last resort?