Investigators questioned Vice President Dick Cheney (search) recently in the probe of who in the Bush administration leaked the name of a covert CIA operative last year, a source familiar with the investigation said Saturday.

The interview of the vice president follows an acknowledgment by President Bush that he has consulted with a private attorney regarding the probe, indicating that Bush, also, expects to be questioned.

A federal grand jury in recent months has questioned numerous White House and administration officials to learn who revealed the name of CIA operative Valerie Plame (search), wife of former Ambassador Joseph Wilson (search), to the news media.

Disclosure of an undercover officer's identity can be a federal crime.

Cheney's office said earlier this week that if the vice president were to seek counsel on any issue, he would turn to Terrence O'Donnell (search), a senior partner in the Washington law firm of Williams & Connelly. Cheney has consulted with O'Donnell for years.

"Given the fact that there is an ongoing investigation, it is appropriate to refer requests for comment to the Office of Special Counsel," said Cheney spokesman Kevin Kellems.

U.S. Attorney Patrick Fitzgerald of Chicago, whose office declined to comment, was chosen to run the investigation in late December after Attorney General John Ashcroft disqualified himself from the politically sensitive case to avoid an appearance of conflict of interest.

Cheney was not under oath when he was questioned, according to the source, who spoke on condition of anonymity because the investigation involves a criminal matter. The source did not know what Cheney said or what he was asked or whether he had an attorney present. But the central issue of the investigation is who disclosed Plame's name.

Syndicated columnist Robert Novak revealed Plame's work for the CIA a week after Wilson publicly criticized Bush's claim that Iraq had tried to obtain uranium from the African nation of Niger.

Wilson had earlier been sent to Niger by the CIA to check out the allegation and concluded it was unfounded. Bush stated subsequently in his State of the Union address that Iraq had sought to buy uranium in Africa.

Wilson says revealing his wife's name was an attempt to discredit him. In printing Plame's name, Novak wrote that two administration officials said Wilson's wife suggested sending him on the Niger trip.

Wilson has suggested in a book that the leaker was Lewis "Scooter" Libby (search), Cheney's chief of staff.

The White House denies the claim and accuses Wilson of seeking to bolster the campaign of Democrat John Kerry, for whom he has acted as a foreign policy adviser.

The interview of Cheney was first reported by The New York Times on Saturday.

A number of news organizations have received federal subpoenas to face questioning about the alleged leak.

Justice Department guidelines for criminal prosecutions state that all avenues should be explored before reporters are subpoenaed or approached in an investigation. So the issuing of subpoenas for reporters may indicate the investigation is nearing an end.