Vice President Cheney's recent interview with representatives of a special prosecutor looking into the leak of a covert CIA officer's name is the latest suggestion that the grand jury probe is in a highly active phase.

News of the Cheney interview, confirmed yesterday by a government official who was briefed on it and who refused to be identified publicly, comes on the heels of last week's disclosure that President Bush has lined up a private attorney in case special prosecutor Patrick J. Fitzgerald seeks to question him about the public disclosure last summer of the identity of CIA employee Valerie Plame. The grand jury investigation, now in its sixth month, has for the most part been conducted in extraordinary secrecy because it involves a national security matter.

In recent weeks, however, prosecutors have subpoenaed at least two reporters and sought to interview others in an effort to learn whether Plame's identity was intentionally disclosed by administration officials who sought to cast doubt on the credibility of her husband, former ambassador Joseph C. Wilson IV.

In 2002, the CIA sent Wilson to the African nation of Niger to investigate claims that Iraqi President Saddam Hussein had tried to buy uranium there. The agency asked Wilson to make the trip after Cheney asked for more information about the Niger claims. Wilson, a critic of the Iraq war, publicly charged a year ago that the administration had exaggerated Iraq's efforts to develop weapons of mass destruction.

Last July, syndicated columnist Robert D. Novak wrote that two administration officials told him Wilson was selected for the mission by his wife, Plame, a CIA specialist on weapons of mass destruction. Disclosure of a covert officer's name is a criminal act if it is done intentionally by someone authorized to have the information.

Lawyers representing witnesses in the case said the latest flurry of witness interview requests could signal that prosecutors are about to bring the investigation to a close. Several lawyers said they expect Fitzgerald would want to talk to Bush and Cheney no matter how his investigation comes out in the end.

"It was inevitable he would talk to both of them," one lawyer said. He, like other lawyers in the case, asked not to be quoted by name.

The White House declined to comment on Cheney's interview with prosecutors, which was first reported Friday night by the New York Times, or to say when it occurred. Cheney's office referred inquiries to Fitzgerald's office, which has declined to comment on any aspect of the investigation. Cheney's attorney, Terrence O'Donnell, did not return phone calls for comment.

Vice President Cheney has been interviewed by investigators.