Vice President Cheney's former chief of staff lied to investigators about his role in leaking a CIA officer's identity in order to keep his job and protect the White House from political embarrassment, prosecutors told jurors yesterday in the closing arguments of I. Lewis "Scooter" Libby's perjury trial.

Pointing to a courtroom screen showing eight witnesses who contradicted Libby, Special Counsel Patrick J. Fitzgerald said it was no coincidence that Bush administration colleagues and reporters recalled Libby as intensely focused on undercover CIA officer Valerie Plame early in the summer of 2003, as her husband was publicly challenging the White House's rationale for going to war in Iraq.

"This is something important, something he was focused on, something he was angry about," Fitzgerald said. "He had a motive to lie, and . . . he stole the truth from the justice system."

Libby "told a dumb lie and got caught" when leak investigators refused to go away, Fitzgerald said. He added that Libby's lies had "left a cloud over the vice president" because Cheney's role in the leak remained unclear.

But two defense attorneys argued that Libby was a harried and hardworking public servant who was guilty only of forgetfulness about a relatively insignificant matter given his pressure-cooker job.

In impassioned, and at times disjointed arguments, the defense lawyers drew attention to numerous witnesses who had faulty or questionable memories and conflicting recollections. They said it was unfair to assume that the witnesses had made honest mistakes but that Libby's untruths were deliberate.

"If you're not sure, that's not guilty," said attorney Theodore Wells Jr. "It's impossible to say with any degree of certainty that Mr. Libby is engaged in intentional lying."

Libby is charged with five felonies: two counts of lying to FBI agents, two counts of perjuring himself in grand jury testimony and one count of obstructing the federal probe into whether Bush administration officials illegally leaked classified information by disclosing Plame's identity to reporters.

They say Libby lied when he told investigators he learned about Plame from NBC's Tim Russert and passed it along as unconfirmed gossip.

Libby has pleaded not guilty, contending he inaccurately remembered conversations that he recounted to FBI agents and a grand jury. No one is charged with the leak itself.

The 12-member jury will receive instructions from presiding U.S. District Judge Reggie B. Walton early today about how to weigh the high-profile case against Libby. Jurors are expected to begin deliberations before noon.

Plame is married to former ambassador Joseph C. Wilson IV, whose accusations in 2003 that the Bush administration twisted intelligence to justify the war with Iraq set in motion events leading to the leak of his wife's name in a syndicated column by Robert Novak. Wilson's claims infuriated Cheney and others in the White House, and Cheney deputized Libby to contact reporters and rebut Wilson's claims.

Wilson turned out to be a potent critic. He had been sent to Niger by the CIA a year earlier to check on reports that Iraq had tried to obtain material for nuclear weapons there, and concluded that the reports were false. Within days of Wilson going public about his findings in July 2003 , the White House acknowledged that President Bush's State of the Union address should not have included the assertion that Iraq was trying to purchase uranium.

Fitzgerald told the jury yesterday that Libby was engaged in a campaign to make reporters skeptical of Wilson. His wife's post at the CIA and her role in suggesting him for the mission became a useful tool to insinuate that he wasn't qualified for the mission to Niger. The prosecutor disputed the defense's argument that Libby did not remember Plame because she was so trivial to him.

"To [Libby] she wasn't Valerie Wilson, she's wasn't a person," the prosecutor said, sipping from a plastic cup of water as he walked back and forth in front of the jury box. "She was an argument, a fact to use against Joe Wilson."

Prosecutor Peter Zeidenberg, summing up the government's evidence, said Libby "absolutely fabricates two conversations that never happened" -- with Time magazine reporter Matt Cooper and NBC's Russert. He said Libby's claim that he didn't remember the conversations was "just not credible" because Cheney considered the matter very important and it commanded much of Libby's time.

Zeidenberg also said Libby had several motives to lie. The president had said he would fire whoever had disclosed Plame's identity, a criminal investigation had begun, and, at Libby's urging, Cheney had personally vouched for Libby, getting the White House to say publicly that Libby was not the leaker.

In the defense's closing argument, Wells countered that the case was simply "he said, she said." He contended that it was "madness" to try to convict Libby of a crime based on his foggy memory about fragments of conversations that were the subject of FBI questions three and four months after they took place.

"It's a case about different recollections between Mr. Libby and some reporters," Wells said. "This is an important trial, and I represent an innocent man."

Wells said that Libby honestly believed he learned about Plame for the first time from Russert in a July 10, 2003, conversation -- a month after he was actually told about her by the vice president, Libby later acknowledged. Wells emphasized to the jury that Russert first told the FBI that he couldn't completely rule out discussing the subject with Libby because he talks to so many people.

"That's reasonable doubt right there," Wells said of an FBI agent's notes. "If you say, 'I believe Mr. Russert beyond a reasonable doubt,' my client's life would be destroyed. His reputation would be destroyed."

Defense attorney William Jeffress Jr. reminded the jury of the pointed questioning that Libby endured when Fitzgerald asked Libby several different ways about nearly every conversation he had in a two-month period in 2003.

"It's not easy being in a grand jury. And Mr. Libby was there for eight hours," Jeffress said. "If he got something wrong in eight hours of questioning, that wasn't an intentional lie. Which witness came in here that didn't get something wrong?"

Jeffress highlighted the conflict between testimony of former White House press secretary Ari Fleischer, who said he had not told Washington Post reporter Walter Pincus about Plame, and Pincus's account, in which Fleischer was his source for that information. Jeffress said there were a lot of possible explanations, including that Fleischer lied.

"Of course, possibilities don't cut it in a criminal case," Jeffress said.