A House committee chairman said Tuesday he is seeking more documents from the CIA leak probe because of significant disclosures to the FBI by Vice President Dick Cheney's former chief of staff and new details about Cheney's role in the scandal in a book by a former White House press secretary.

The request to the Justice Department by Rep. Henry Waxman follows a review of edited FBI reports and publication of a book by President Bush's former spokesman Scott McClellan, who has said he was misled by others, possibly including Cheney, about the role of I. Lewis "Scooter" Libby in leaking CIA operative Valerie Plame's identity.

Waxman, D-Calif., sent a letter to the Justice Department after learning that Libby, Cheney's former top aide, told the FBI that it's possible he was instructed by Cheney to disseminate information to the press about Plame, the wife of Bush administration war critic Joseph Wilson.

"This is a significant revelation and, if true, a serious matter," Waxman wrote Attorney General Michael Mukasey.

Waxman's request was fueled in part by McClellan's book, in which he describes how he was instructed to respond to press inquiries about Libby's role in the Plame leak. McClellan has said publicly in recent days that Bush and Cheney "directed me to go out there and exonerate Scooter Libby."

"It would be a major breach of trust if the vice president personally directed Mr. McClellan to mislead the public," said Waxman, who chairs the House Oversight and Government Reform Committee.

Waxman said Libby's comments about Cheney were included in an edited version of an FBI interview report provided to the committee. Waxman now wants access to FBI summaries of any interviews with Bush and Cheney as part of the CIA leak investigation.

Plame's CIA identity was leaked to the news media by several top Bush administration officials in 2003, including Libby and former top White House political adviser Karl Rove. Last July, Bush commuted Libby's 2 1/2-year sentence, sparing him from serving any prison time after being convicted of perjury, obstructing justice and lying to the FBI.

Waxman first asked Mukasey for documents six months ago, including FBI interviews of Bush and Cheney. The Justice Department provided edited versions of FBI interview reports with various White House officials including Libby and Rove, but nothing on Bush or Cheney.

Cheney spokeswoman Lea Anne McBride declined to comment, noting a pending lawsuit filed by Plame. The suit accuses Cheney and several administration officials of revealing her identity to reporters.

FBI spokesman Rich Kolko also declined comment. Justice Department spokesman Peter Carr said the department will review Waxman's letter.

There was testimony and documentation at Libby's trial that Cheney knew in mid-June 2003 that Wilson's wife worked at the CIA and told Libby about it. That time frame was more than a month before Plame's CIA identity turned up in a syndicated newspaper column by Robert Novak.

Witnesses testified that Cheney, Libby and other Bush administration officials mounted a campaign to counter criticism by Plame's husband, Wilson, who accused the administration of twisting prewar intelligence to exaggerate the Iraqi threat.

At Libby's trial, Cheney's spokeswoman, Cathie Martin, testified that Cheney personally wrote out statements and talking points for Libby and other aides to give to reporters to rebut Wilson's allegations.