WASHINGTON — When Vice President Dick Cheney's former chief of staff goes on trial today on charges of lying about the disclosure of a CIA officer's identity, members of Washington's government and media elite will be answering some embarrassing questions as well.

The estimated six-week trial of I. Lewis "Scooter" Libby will pit current and former Bush administration officials against one another and, if Cheney is called as expected, will mark the first time a sitting vice president has testified in a criminal case.

It also will force the media into painful territory, with as many as 10 journalists called to testify for or against an official who was, for some of them, a confidential source.

Besides Cheney, the trial is likely to feature government and media luminaries including NBC's Tim Russert, former White House spokesman Ari Fleischer, columnist Robert Novak and Washington Post Assistant Managing Editor Bob Woodward.

Special Counsel Patrick Fitzgerald's investigation into the leak of CIA officer Valerie Plame's identity took an ominous turn in the summer of 2004, when reporters were first ordered under threat of jail to reveal their anonymous sources in the administration.

In October 2005, Libby was indicted on charges of perjuring himself before a grand jury, making false statements to investigators and obstruction of justice (though he was not one of the leakers to Novak, who first disclosed Plame's identity).

The government alleges Libby was involved in a concerted White House effort to discredit Plame's husband, former U.S. ambassador Joseph Wilson, who had publicly accused the Bush administration of twisting information he provided on Iraq's nuclear-weapons program.

Wilson led a CIA-sponsored mission to Niger a year earlier and found no grounds for claims that Iraq was trying to obtain uranium there.

Eight days after Wilson went public with his claims, Plame's identity as a CIA officer appeared in Novak's column.

The defense says neither Libby nor the White House sought to retaliate against Wilson and that Libby misspoke to investigators looking into the disclosure because he was overwhelmed by a crush of national security and other matters. He has said he had no motive to lie about the details or timing of conversations with reporters.

The case has largely played out in below-the-radar court hearings as prosecutors and defense lawyers have mapped the boundaries of the trial. Despite speculation that Bush would pardon Libby to avoid the spectacle of a trial, the date has arrived.

Presiding U.S. District Judge Reggie Walton and lawyers for both sides will begin selecting 12 jurors along with alternates today. It is not expected to be an easy task, given the heavy publicity and the involvement of two institutions — the government and the news media — low in the public's esteem.

Walton has assembled 100 prospective jurors and has a pool of 100 more standing by.

He has also girded for intense media coverage, last week issuing unusually strict orders that bar attorneys from commenting publicly during the trial.

Fitzgerald's probe focused on a tense time in Washington, starting in May 2003, when the administration sought to defend its invasion of Iraq even as U.S. troops failed to find weapons of mass destruction, which the administration had cited as one of the main reasons for deposing Saddam Hussein.

That month, reporters began writing about anonymous accusations from Wilson that Bush had sold the war to the public using intelligence Wilson had found to be groundless. Wilson went public with his accusations during the first week of July.

On July 14, Novak published a column identifying Wilson's wife, Plame, as a CIA employee who helped arrange her husband's trip to investigate the Iraq claim. He cited two administration sources.

The government alleges that before Novak's column appeared, Libby set out to discredit and silence Wilson after Cheney shared his irritation about Wilson's claims and Plame's CIA role.

Libby asked State Department and CIA officials for more information about Wilson's mission and Plame, prosecutors say, then shared Plame's role with a New York Times reporter, Judith Miller. At the time, Miller was trying to defend her own reporting, which had asserted evidence that Iraq had weapons of mass destruction.

"It is hard to conceive of what evidence there could be that would disprove the existence of White House efforts to 'punish' Wilson," Fitzgerald wrote in a court filing last year.

Later, when a leak investigation was opened, prosecutors allege Libby lied to FBI agents, telling them he had learned about Plame from Russert in a telephone call on July 10 or 11 and that he had passed along that information as unconfirmed gossip to two other reporters.

The plainspoken Russert will be a star government witness. He has told Fitzgerald that Libby fabricated parts of a conversation with him. He has said that when he spoke with Libby in mid-July, Plame never came up as Libby complained that MSNBC host Chris Matthews had an antiwar slant.

Russert has said he did not know about Plame until he read Novak's column. A source familiar with the case says his version will be corroborated by testimony from NBC News' former president, Neal Shapiro.

Russert told Shapiro about Libby's complaint soon after the call, the source said, saying nothing about Plame.

Miller will be a key, if hostile, government witness. She went to jail for 85 days rather than reveal her talks with Libby. After details of her reporting methods came out in Fitzgerald's probe, she was assailed by media critics and eventually left the Times.

Another crucial set of witnesses is the eight people who worked in the administration with Libby, who collectively describe him as meticulous about details and keen to obtain and spread information about Wilson and Plame before his July 10 call to Russert.

Randall Eliason, a former chief of public-corruption cases in the U.S. Attorney's Office, said the evidence appears to make it difficult for Libby to claim forgetfulness. "You have the vice president cutting out a section of the newspaper, circling it and saying, 'Let's find out about this.' You don't rise to the level of being the vice president's chief of staff by letting that kind of thing slip your mind."

The defense contends Libby forgot how he learned Plame's identity and misspoke when questioned twice by the FBI and twice by a grand jury about his conversations with reporters. He insists there was no cabal to "get" Wilson and that Cheney wanted him only to rebut what he saw as inaccuracies by Wilson.

That Novak first learned about Plame from Richard Armitage, then deputy secretary of state and a skeptic of the war, proves there was no conspiracy, the defense insists.

"Mr. Libby will counter by showing that when he spoke to the FBI and the grand jury, he knew that he was not a source for the public disclosure of Ms. Wilson's employment," his defense lawyers wrote in a recent filing.

Libby's attorneys have said they plan to call Cheney as a witness, presumably to help establish Libby was indeed engulfed by national security matters and had no motive to lie. It is a bold move. The sharp-tongued Cheney could be questioned by Fitzgerald, one of the nation's best prosecutors.

Another key witness for the defense will be Woodward, who after the bulk of the probe was over told Fitzgerald that, a month before Novak's column appeared, he learned of Plame's CIA role from an offhand comment Armitage made while Woodward was interviewing him for a book.

He has said he interviewed Libby soon thereafter and cannot rule out the possibility he talked to him about Plame's identity.

That could buttress Libby's claim that Plame's identity was already known by reporters, so there was no reason for him to lie about discussing it with them.