WASHINGTON — A former vice presidential aide, I. Lewis “Scooter” Libby, acknowledged that he may have discussed with Vice President Cheney whether to tell reporters that a prominent war critic’s wife worked at the CIA, an FBI agent testified yesterday.

Special Prosecutor Patrick Fitzgerald showed the jury video of then-White House press secretary Scott McClellan saying President Bush would fire anyone who was found to have leaked classified information. The video also showed Mr. McClellan saying he had been assured that Mr. Libby did not leak classified information.

Mr. McClellan spoke in October 2003, shortly before Mr. Libby was interviewed by the FBI.

Mr. Libby is charged with lying to the FBI and a grand jury about his conversations with reporters concerning CIA operative Valerie Plame and obstructing an investigation of how her identity and CIA job were leaked to the press in 2003. Mr. Fitzgerald said Mr. Libby’s motive was to avoid being fired.

Mr. Libby’s acknowledgment of a possible discussion with Mr. Cheney about disclosing Ms. Plame’s job is likely to have more impact on political debate about the Plame leak than on the trial because Mr. Libby is not charged with the actual leak.

Agent Deborah Bond was asked whether Mr. Libby described for the FBI details of his talk with Mr. Cheney or any decisions he and Mr. Cheney may have reached. Mr. Libby denies he leaked the name.

Ms. Bond said that during Mr. Libby’s second FBI interview in his office on November 23, 2003, Mr. Libby described flying back from Norfolk, Va., with Mr. Cheney on July 12, 2003, at the height of public controversy over allegations made by Ms. Plame’s husband — a former ambassador, Joseph Wilson.

Mr. Libby told the FBI he went to the front of the plane to get a statement Mr. Cheney wanted released to the press. It denied Mr. Wilson’s suggestion that Mr. Cheney was behind Mr. Wilson’s trip to Niger in 2002 to investigate a report that Iraq was trying to buy uranium there for nuclear weapons.

Mr. Wilson had said in print and on television on July 6, 2003, that he debunked the uranium report and Mr. Cheney should have known that long before Mr. Bush cited the uranium story in his January 2003 State of Union speech as a justification for war with Iraq.

Ms. Bond testified Libby told the FBI “there was a discussion whether to report to the press that Wilson’s wife worked for the CIA.” She added that Mr. Libby expressed some doubt.

“Mr. Libby told us he believed they may have talked about it, but he wasn’t sure,” she said.

She said Mr. Libby did say he had discussed Mr. Wilson’s wife with Mr. Cheney sometime after discussing her with NBC reporter Tim Russert on either July 10 or 11, 2003.

Ms. Bond said Mr. Libby told the FBI that Mr. Russert asked him if Mr. Wilson’s wife worked at the CIA and that Mr. Libby said he replied that he did not know that. Mr. Libby has claimed he had forgotten by the time of the conversation with Mr. Russert that he had earlier learned Ms. Plame’s job from Mr. Cheney around June 12, 2003.

Mr. Libby told the FBI that Mr. Russert told him on July 10 or 11, 2003, that she worked at the CIA and “all the reporters knew that,” Ms. Bond testified.

Mr. Libby told the FBI “he was surprised and it was the first time he heard it,” Ms. Bond testified.