When the jury in I. Lewis "Scooter" Libby's perjury trial returns with its verdict, its decision also will intensify the debate over whether Special Counsel Patrick J. Fitzgerald should have brought the case in the first place.

For Fitzgerald, who has led the CIA leak investigation for more than three years, an acquittal for Vice President Cheney's former chief of staff would be a blow to a reputation as a nonpartisan prosecutor with a record of high-profile successes. Some say it would vindicate critics who think Fitzgerald went too far by charging Libby with perjury when no one was indicted for the original offense investigated, the leak of an undercover CIA officer's name.

"The stakes are enormously high," said Robert Mintz, a former federal prosecutor and now a defense lawyer. If Fitzgerald loses this case, Mintz said, "some will say he lost his way in his search for truth, just another case of a prosecutor who sets off and thinks they can't come back unless they have a prosecution, no matter how trivial."

But several lawyers monitoring the trial as spectators say Fitzgerald has presented a compelling case that the government had a duty to bring.

A federal court jury began deliberating Wednesday about whether Libby intentionally lied about his conversations with reporters and his role in disclosing the identity of CIA officer Valerie Plame in the summer of 2003.

Fitzgerald's investigation shined a spotlight on Cheney's strong interest in rebutting a war critic, the White House's case for war with Iraq, the conduct of top officials and the Washington press corps.

Fitzgerald, 46, the U.S. attorney in Chicago, was appointed special counsel in 2003, heralded as an impartial prosecutor with "a virtually unblemished reputation," Mintz said. Those were important qualities in an investigation enmeshed in partisan politics.

His previous victories include convicting Sheik Omar Abdel Rahman in the 1993 World Trade Center bombing case and compiling the first criminal indictment against Osama bin Laden. But in 2003 he was forced to drop key terrorism counts against the leader of a Muslim charity, Enaam Arnaout, who was convicted of related crimes and imprisoned.

Fitzgerald's motives and credentials were challenged when his investigation homed in on top Bush administration officials, including senior White House adviser Karl Rove, as well as the Washington press corps. In a showdown with the New York Times, Fitzgerald went to the Supreme Court to force reporters to divulge their confidential conversations with government sources.

In October 2005, nearly two years after the investigation began, Fitzgerald charged Libby, 56, with making false statements, perjury and obstruction of justice -- but did not accuse anyone of intentionally blowing Plame's cover. He said Libby's lies made it impossible to know whether he had intended to commit that crime.

Fitzgerald alleged that Libby lied about sharing information about Plame with reporters and had been part of a campaign to discredit Plame's husband, former ambassador Joseph C. Wilson IV. The CIA sent Wilson to Niger in 2002 to investigate allegations that Iraq was attempting to obtain nuclear material there. Wilson found the reports groundless and in 2003 publicly accused President Bush of twisting his report's conclusions to help justify the war.

Former senator Fred Thompson said that win or lose, Fitzgerald will be judged as a prosecutor run amok who chased petty political crimes "to the ends of the Earth."

"He had to realize early on that the matter he was appointed to investigate was not a crime," said Thompson, who is a board member of a group raising legal funds for Libby. "He should have put his little papers in his briefcase and gone back to Chicago."

Mary Jo White, a former U.S. attorney who worked with Fitzgerald on the World Trade Center case, said the pressure on Fitzgerald is magnified because his investigation reached Bush and Cheney, both of whom were questioned. Opponents and supporters of Bush, the war and the investigation will be rooting for vindication in the verdict, she said.

"Any case that is as high-profile as this is important to win because of how it will be portrayed -- and misportrayed," White said. But she said that judges and defense lawyers consider Fitzgerald a straight shooter and that that will not change.

The trial has given Fitzgerald chances to show his well-known mastery of facts and his expertise at cross-examination.

When Libby's former deputy, John Hannah, testified for the defense on the overwhelming nature of Libby's job, Hannah said that at the time, Libby was monitoring al-Qaeda plots, the Iraq war and other national security threats.

Hannah, who said he was lucky to get a few minutes to talk to Libby, was supposed to help buttress Libby's argument that he had more important things to remember when he spoke to investigators than conversations with reporters.

With two quick questions, Fitzgerald drew Hannah to the week of July 6, 2003, when, the jurors had been told, Libby met for two hours with Times reporter Judith Miller to complain about Wilson.

"And so, if you look at what was going on . . . if he gave someone an hour or two during that week, it was something that Mr. Libby thought would be important, correct?"

Hannah paused, but had to agree: "With regard to me, yes."

Despite his seriousness, Fitzgerald also has shown a sense of humor. He warned U.S. District Judge Reggie B. Walton that playing an interview from the "Imus in the Morning" radio show would be problematic because "there's no Imus exception to the hearsay rule."

Washington lawyers who have dropped in to watch the case say Fitzgerald's skills were best demonstrated in the tapes played in court of him questioning Libby before a grand jury. Under relentless questioning, Libby explained over nearly an hour that he forgot he learned about Plame from Cheney, then believed he learned it for the first time from NBC's Tim Russert, but recalled that Cheney did not share classified information. Libby's voice increasingly faded in strength, as Fitzgerald made him sound more and more illogical.

"And so when Tim Russert had this conversation with you, you didn't remember that the vice president told you in June that Wilson's wife works at the CIA," Fitzgerald said, "but when you remembered what you forgot, you remembered that you learned it in June not to be classified."

He paused, then asked incredulously: "As you sit here today, is that your testimony under oath?"

Staff researcher Julie Tate contributed to this report.