NBC's Tim Russert got the sort of Meet the Press interrogation he usually gives his guests as attorneys Thursday flashed excerpts of his previous statements on a video monitor and asked him to explain inconsistencies.

Russert is the final witness for the prosecution in the perjury trial of former White House aide I. Lewis (Scooter) Libby. The broadcast journalist, who hosts the Sunday network-television interview show, found his own scruples questioned during his second day on the witness stand.

Russert seemed uncomfortable at times as Libby's attorneys asked him to explain why he willingly told an FBI agent about a July 2003 conversation with Libby, then gave a sworn statement saying he would not testify about that conversation because it was confidential.

"Did you disclose in the affidavit to the court that you had already disclosed the contents of your conversation with Mr. Libby?" Libby attorney Theodore Wells asked.

"As I've said, sir…" Russert began.

"It's a yes or no question," Wells interrupted.

"I'd like to answer it to the best of my ability," Russert said.

"This is a very simple question; either it's in the affidavit or it's not," Wells said. "Did you disclose to the court that you had already communicated to the FBI the fact that you had communicated with Mr. Libby?"

"No," Russert said.

Wells wants to cast Russert as someone who cannot be believed, who publicly championed the sanctity of off-the-record conversations but privately revealed information to investigators.

Russert said he viewed the FBI conversation and testimony to prosecutors differently.

Russert, Libbytell different stories about phone call

Russert's credibility is under fire because he and Libby tell very different stories about a July 2003 phone call that is at the heart of the case. The question of who to believe could be a critical issue for the jury.

Both men agree that Libby called Russert to complain about a colleague's news coverage. Libby says at the end of the call, Russert told him "all the reporters know" that Valerie Plame, wife of a prominent war critic, worked for the CIA. Russert testified that he never said that.

"That would be impossible," Russert testified Wednesday. "I didn't know who that person was until several days later."

Libbygave the information about Plame to other journalists, always with the caveat that he had heard it from reporters, he has said. Prosecutors say Libby concocted the Russert conversation to shield himself from prosecution for revealing classified information he was given by government sources.

Libby's attorneys say Russert knew about Plame from colleague Andrea Mitchell. Mitchell said in an interview that she and other reporters knew Plame worked for the CIA but she later recanted that statement.

Wells had hoped to play clips of Mitchell discussing her statements on the Don Imus morning show on MSNBC. Special prosecutor Patrick Fitzgerald successfully argued that the tapes shouldnot be played.

"We might as well take 'Wigmore on Evidence' and replace it with 'Imus on Evidence,"' Fitzgerald said, referencing the classic treatise on evidentiary law. "There's no Imus exception to the hearsay rule. This has no business in a federal court."

Wells has questioned Russert about other phone conversations he couldn't remember, inconsistencies between his current account and FBI notes of an agent's original interview with him, and the likelihood that he would have let such a high-ranking official off the phone without fishing for some news.

Libby's attorneys also will try to undercut the credibility of former New York Times reporter Judith Miller, who testified that Libby revealed Plame's identity to her. Defence attorney William Jeffress said he intends to call Miller's former boss, Times managing editor Jill Abramson, to try to refute Miller and question her credibility.