WASHINGTON — The reputation of one of America’s most prominent journalists, Tim Russert of NBC News, came under fire yesterday as a lawyer for I. Lewis Libby Jr. sought to cast doubt on Mr. Russert’s account of a conversation with the former vice presidential aide.

Mr. Russert testified that Mr. Libby called him in July 2003 to complain about the MSNBC program “Hardball,” but said the two men never discussed the wife of a former American ambassador, Joseph Wilson IV, or that she worked for the CIA.

The leaked identity of Mr. Wilson’s wife, Valerie Plame, sparked a criminal investigation, and Mr. Libby is on trial for allegedly lying to federal investigators and a grand jury during that inquiry.

Mr. Libby has sworn under oath that he learned about Ms. Plame from Mr. Russert, a claim that the NBC newsman and “Meet the Press” moderator said repeatedly yesterday was “impossible.”

“I didn’t know who that person was until several days later,” Mr. Russert testified. The telephone conversation occurred on or about July 10, 2003, although Mr. Russert said he couldn’t remember the exact day or time it took place. He said he first became aware of Ms. Plame and her CIA affiliation when he read a column by Robert Novak on July 14, 2003, which publicly disclosed her identity for the first time.

For Mr. Russert, the host of America’s most watched Sunday morning interview program, the court appearance was the ultimate role reversal. He spoke calmly and directly, but jurors rarely heard the authoritative tone and cadence so familiar to viewers of “Meet the Press.”

Reporters and onlookers packed the courtroom in anticipation of Mr. Russert’s testimony, the last in a line of prominent prosecution witnesses who have offered an often hidden view of the relationship between the White House and the Washington press corps. Mr. Russert walked in using a crutch, saying he was recovering from a broken ankle suffered 10 weeks ago. At times he appeared in physical discomfort getting on and off the witness stand.

The lead defense attorney, Theodore Wells Jr., took little pity on Mr. Russert’s condition as he sought to pit the journalist’s claims about his conversation with Mr. Libby against his reputation as an aggressive, hard-hitting reporter.

At issue was Mr. Russert’s assertion that during the phone call with Mr. Libby, he never asked the then-chief of staff to Vice President Cheney about Mr. Wilson, who had been at the center of the news that week after he published an opinion piece on July 6 that criticized the Bush administration’s justification for the Iraq war.

Seeking to establish Mr. Russert’s high-profile status and competitive nature as a journalist, Mr. Wells made reference to passages in his 2004 book, “Big Russ and Me,” in which Mr. Russert describes his habit of talking to as many people as he can when pursuing a story in order to “get it first.”

Mr. Wells asked Mr. Russert how, given his approach to journalism, he could talk to a top White House official and not ask for more details on a major story of the day.

“You had the chief of staff of the vice president on the phone, and you didn’t ask him one question on the Wilson issue?” Mr. Wells asked, his voice rising in apparent disbelief.

“It was very much in a listening mode,” Mr. Russert replied in an even tone, saying Mr. Libby was “very agitated” and “not in a mood to talk.” He described the call not as one from a source, but as a “viewer complaint” in which Mr. Libby was criticizing an edition of “Hardball” that aired earlier in the week and had focused heavily on Mr. Wilson’s claims.

Mr. Russert, who has been the Washington bureau chief of NBC News since 1989, said he urged Mr. Libby to talk to other senior executives at the network who had more control over the MSNBC show, which is hosted by Chris Matthews.

The exchange between Messrs. Russert and Wells became tense at times, as Mr. Russert struggled to recall specific points of his prior interactions with investigations and asked to see copies of his statements. “I’m not going to give it to you right now, okay? I want to test your memory,” Mr. Wells said at one point.

The moment played into a consistent strategy by the defense to expose the faulty recollections of prosecution witnesses. Mr. Libby’s own memory lapses are a central argument in rebutting the accusation that he deliberately misled federal investigators probing the CIA leak.

Mr. Libby initially told the FBI that he first learned about Ms. Plame from Mr. Russert, but he later said he forgot about an earlier conversation he had about her with Mr. Cheney.

His lawyers have argued that he was simply too busy to remember details of conversations he had with reporters and government officials. Mr. Russert took the stand after the prosecution finished playing hours of tapes of Mr. Libby’s grand jury testimony. The defense is expected to call its first witness late this afternoon after Mr. Russert finishes his testimony and the prosecution rests.

LISTEN TO LIBBY’s GRAND JURY TESTIMONY

Part One

http://wid.ap.org/documents/libbytrial/feb7/GX1T.mp3

Part Two

http://wid.ap.org/documents/libbytrial/feb7/GX2T.mp3