WASHINGTON — The special prosecutor in the CIA leak case, Patrick Fitzgerald, is suggesting in his strongest terms yet that Vice President Cheney was involved in an effort to unmask a CIA operative married to an administration critic.

Mr. Fitzgerald’s explosive comments came as he delivered closing arguments yesterday in the monthlong obstruction-of-justice and perjury trial of Mr. Cheney’s former chief of staff, I. Lewis Libby Jr.

“There’s a cloud over the vice president,” Mr. Fitzgerald told the jury. “We didn’t put that cloud there. That cloud’s there because the defendant obstructed justice. That cloud is something you just can’t pretend isn’t there.”

The prosecutor also asserted that Mr. Libby violated a request from investigators by discussing his recollections about the case with his boss, Mr. Cheney, while the probe was under way. “He’s not supposed to be talking to other people,” Mr. Fitzgerald said of Mr. Libby. “The only person he told is the vice president. … Think about that.”

Broadening his attack on the White House, Mr. Fitzgerald took a shot at President Bush, indirectly criticizing him for not firing officials implicated in the leaks about the CIA officer, Valerie Plame. The prosecutor noted that in 2003 the White House press secretary, Scott McClellan, said Mr. Bush would immediately dismiss anyone involved in leaking Ms. Plame’s identity.

“Any sane person would think, based on what McClellan said in October 2003, that any person involved in this would be fired,” Mr. Fitzgerald said.

The prosecutor’s clear implication was that Mr. Bush failed to keep his word. Mr. Bush’s top political aide, Karl Rove, is still working at the White House despite having served as a source for two press accounts about Ms. Plame. A State Department official who leaked Ms. Plame’s identity at least twice, Richard Armitage, resigned at the end of 2004. Mr. Libby, who quit after being indicted, has conceded discussing the CIA staffer with a Time magazine reporter, Matthew Cooper.

Mr. Libby faces five felony charges stemming from claims that he lied to the FBI and a grand jury about his conversations with Mr. Cooper and NBC’s Washington bureau chief, Timothy Russert. No one was charged criminally for the leaks.

Mr. Libby’s lead defense counsel, Theodore Wells Jr., said prosecutors constructed a flimsy case by assuming that the reporters are telling the truth and Mr. Libby is lying. The defense lawyer noted that the government had no direct evidence that Mr. Libby set out to deceive anyone.

“There’s no recording. There aren’t any notes. There’s nothing,” Mr. Wells said. He called the prosecution case “madness” and warned jurors that they were facing a grave decision that they might come to regret.

“The stakes are a man’s reputation, a man’s life,” Mr. Wells said. “Once you check that box, he’s got to live with that forever, and so do you.”

The defense attorney also warned jurors, who hail from the capital’s predominantly liberal populace, against allowing their personal politics to color their view of the case. “If somebody starts to say, ‘He’s a Republican. He worked for Cheney. Let’s do him.’ Help that person,” Mr. Wells said. “Don’t sacrifice Scooter Libby in this case based on the way you feel about the war in Iraq or how you feel about the Bush administration.”

Mr. Wells became emotional as he concluded his argument with a plea to spare Mr. Libby. “Get him back to work. Give him back to me,” Mr. Wells said as his voice trailed off and he began to tear up. He then took a seat at the defense table. The veteran defense attorney sat silently there for several minutes, ignoring his colleagues and alternately staring at the back wall of the courtroom and his lap.

Mr. Fitzgerald rejected the defense’s contention that the case against Mr. Libby be examined on a witness-by-witness basis. The prosecutor said Mr. Libby’s claim that he thought he learned of Ms. Plame’s identity from Mr. Russert was impossible to believe given the variety of witnesses from inside and outside the White House who claim to have discussed the matter with Mr. Libby.

“It’s not one on one. It’s not, ‘He said, she said,'” Mr. Fitzgerald said. “Nine witnesses can’t all misremember.”

Mr. Fitzgerald said it was evident that Mr. Libby was angry at Ms. Plame’s husband, Joseph Wilson IV, who had claimed in an op-ed piece and a television appearance that Mr. Bush lied by claiming in his 2003 State of the Union address that Iraq sought nuclear materials in Africa.

“We all know that when you’re angry at someone, you remember,” the prosecutor said, poking at the defense’s contention that Mr. Libby may have forgotten several of his conversations on the subject.

Mr. Fitzgerald also dissected White House talking points and concluded that Mr. Cheney was honing in on Ms. Plame, whom the vice president suspected arranged for her husband to take a trip to Africa at the CIA’s expense. At one point in July 2003, “the question of who sent Mr. Wilson on his trip is the no. 1 question on the vice president’s mind,” the prosecutor said.

The defense argued repeatedly yesterday that the prosecution has failed to prove its case against Mr. Libby beyond a reasonable doubt. Defense attorneys have their strongest argument on that point with respect to the two counts based solely on the differences between Mr. Libby and Mr. Cooper. Mr. Cooper remembers getting what he took as a brief, vague confirmation of Ms. Plame’s employment. Mr. Libby contends that he gave a lengthier explanation, saying he had heard about Ms. Plame from reporters, didn’t know whether she actually worked at the CIA, and didn’t even know whether Mr. Wilson had a wife.

The prosecution’s case regarding Mr. Libby’s contact with Mr. Russert may be more successful because it is not entirely contingent on Mr. Russert’s claim never to have discussed Ms. Plame with Mr. Libby. The indictment also faults Mr. Libby for telling the FBI and the grand jury that he was taken aback when Mr. Russert mentioned Ms. Plame. The prosecution asserts that Mr. Libby could not have been surprised because he had discussed Ms. Plame in the preceding days with other White House officials, a top CIA executive, and a New York Times reporter, Judith Miller.

“You don’t need the Tim Russert evidence to find the defendant guilty,” Mr. Fitzgerald said.

In theory, the former vice presidential aide could be sentenced to up to 30 years in prison if he is convicted on all five counts. His actual sentence would almost certainly be much lighter, based on guidelines that take into account his lack of a prior criminal record and other factors.

Mr. Wells told jurors yesterday about the “permanency” of a guilty verdict in the case. However, many commentators on the right and the left believe Mr. Bush will pardon Mr. Libby if he is convicted.

The White House has steadfastly refused to comment on the case. Mr. Cheney was traveling in Japan yesterday. Asked about the new aspersions cast on the vice president, a spokeswoman for Mr. Cheney, Megan McGinn, said he would have no comment while the matter is before the courts.

Mr. Fitzgerald’s pregnant statements yesterday about Messrs. Bush and Cheney may have been intended to bolster the chance of convicting Mr. Libby by tying him to the unpopular political figures atop the executive branch. Another possibility is that the closing statements offered the prosecutor who has headed the investigation for more than three years his last clear opportunity to opine on the actions of the president and the vice president in the case. While prosecutors appointed under the independent counsel law were permitted to file reports on their findings, there is no such provision for Mr. Fitzgerald, a U.S. attorney who was appointed by the Justice Department after senior officials there recused themselves because of the political sensitivity of the case.

Jurors are expected to begin deliberating Mr. Libby’s fate this morning, after receiving final instructions from Judge Reggie Walton.