President Bush was interviewed for more than an hour yesterday by a special prosecutor investigating whether administration officials illegally disclosed the name of a covert CIA officer last summer.

Special prosecutor Patrick J. Fitzgerald and several assistants questioned the president for about 70 minutes in the Oval Office yesterday morning. A White House spokesman declined to comment on the substance of the interview but said Bush, who was accompanied by a private lawyer, was not placed under oath.

Fitzgerald's session with Bush comes amid a flurry of recent interviews and subpoenas from investigators who have operated in almost complete secrecy for six months, giving little outward indication of where the probe is headed. White House counsel Alberto R. Gonzales testified on June 18 before a grand jury taking testimony in the case, and it was revealed in early June that prosecutors had interviewed Vice President Cheney.

"The leaking of classified information is a very serious matter," said White House press secretary Scott McClellan, adding that Bush was "pleased to do his part" to aid the probe.

"No one wants to get to the bottom of this matter more than the president of the United States, and he has said on more than one occasion that if anyone -- inside or outside the government -- has information that can help the investigators get to the bottom of this, they should provide that information to the officials in charge."

Fitzgerald is investigating whether Bush administration officials leaked the name of CIA covert officer Valerie Plame to syndicated columnist Robert D. Novak last July. Plame is married to former ambassador Joseph C. Wilson IV, a public critic of the Bush administration's claims about Iraq's efforts to develop weapons of mass destruction. Wilson has suggested that administration officials disclosed his wife's identity as retaliation for his criticism.

The disclosure of a covert CIA officer's name could be a felony punishable by up to 10 years in prison if it was done intentionally by an official who knew the government was trying to maintain her cover.

The disclosure came in a column Novak published last July 14. He said that when he wondered why the CIA selected Wilson in 2002 to investigate claims that Iraq had tried to buy uranium in Niger, two administration officials told him that Wilson's wife worked at the CIA and set up the trip.

Bush's session with prosecutors is unusual but not unprecedented. Bill Clinton testified or was interviewed at the White House in criminal investigations at least seven times during his presidency, on matters that included a probe of the death of deputy White House counsel Vincent Foster Jr., campaign finance irregularities, the Whitewater inquiry and the Monica S. Lewinsky investigation that led to his impeachment.

"Any careful prosecutor would want to make sure that he or she left no stone unturned. In that sense, an interview with the president should not be seen as out of the ordinary," said Solomon L. Wisenberg, a former prosecutor who investigated Clinton.

Bush retained a private lawyer, James E. Sharp, for the interview. Sharp did not return calls seeking comment yesterday.

Some lawyers representing witnesses in the case have speculated that the recent activity, including the interviews of the president and vice president, may signal that the investigation is close to completion. But others said they are less certain that the interview with senior White House officials represents a tying up of loose ends.

"It's hard to believe the special prosecutor would be burdening the president with an interview unless they had testimony to the effect that the president had information," said Floyd Abrams, a First Amendment lawyer representing Time magazine in the probe.

Fitzgerald has subpoenaed reporters from Time and NBC to testify before the grand jury. Both media organizations are fighting those subpoenas in court. The subpoenas to reporters may be another indication that the probe is nearing an end, because Justice Department guidelines demand that prosecutors exhaust all other avenues before calling reporters before a grand jury.

This week, Fitzgerald took a tape-recorded deposition that will be played to the grand jury from Washington Post reporter Glenn Kessler. Kessler said he agreed to be interviewed, at the urging of I. Lewis "Scooter" Libby, chief of staff to Cheney, about two telephone conversations he had with Libby. Kessler said he told the prosecutors that in conversations last July 12 and July 18, Libby did not mention Plame or Wilson.

Prosecutors were interested in questioning Kessler because a Post story in October that said an administration official told an unnamed Post reporter on July 12 that Wilson's wife set up his trip to Niger.