WASHINGTON — In a major reversal, defense lawyers for I. Lewis Libby Jr. now intend to close their case without testimony from the former White House aide or his onetime boss, Vice President Cheney.

The decisions not to put Messrs. Libby and Cheney on the stand were disclosed by the lead defense counsel, Theodore Wells Jr., yesterday afternoon at Mr. Libby’s trial on felony obstruction of justice, perjury, and false statement charges stemming from an investigation into the disclosure of a CIA officer’s identity.

“We have released the vice president as a potential witness,” Mr. Wells said at a hearing outside the presence of the jury. He said the defense team had recommended to Mr. Libby that he not testify and the former White House aide agreed.

In a brief exchange with Judge Reggie Walton, Mr. Libby confirmed that he understood his right to testify and was waiving it freely. “I will follow the advice of my counsel,” the former chief of staff to Mr. Cheney said.

Neither Mr. Libby nor Mr. Wells offered any explanation for the change of course, which contradicted repeated indications from the defense in recent months that both men were likely to testify.

Prosecutors say Mr. Libby deliberately lied to investigators about his contacts with reporters and government officials regarding the unmasked CIA operative, Valerie Plame. The vice presidential aide was a potential suspect in that probe because he was part of a White House effort to discredit claims by Ms. Plame’s husband, Joseph Wilson IV, that President Bush distorted evidence about Iraq’s nuclear procurement efforts in Africa.

Defense lawyers for Mr. Libby have argued that any misstatements he made to the FBI or the grand jury were the product of memory lapses brought on by the weighty and time-consuming national security matters he was juggling. The defense also has suggested that the journalists and officials who have contradicted Mr. Libby have axes to grind or memory problems of their own.

A former prosecutor in the Justice Department’s public corruption unit, Jonathan Rosen, concurred with the defense’s decision to keep Mr. Libby off the stand.

“I think it’s very astute,” Mr. Rosen said in an interview. The exprosecutor said that if Mr. Libby were to testify, the entire case could ride on his believability, rather than on the broader question of whether the prosecution has met its burden to prove beyond a reasonable doubt that the former Cheney aide intentionally lied.

“The testimony of a defendant can be of such talismanic significance,” Mr. Rosen said. “That, by itself, can result in burden-shifting.”

Legal analysts said defense lawyers were likely concerned that any helpful testimony Mr. Cheney could have provided might have been undercut, or worse, by the vice president’s low approval ratings and heavy political baggage. “I assume that’s part of their calculus,” a law professor at the University of Richmond, Carl Tobias, said.

Another factor may have been fears that Mr. Cheney, who recently grew prickly under questioning by Wolf Blitzer of CNN, might alienate jurors by reacting sharply to challenging cross-examination by the lead prosecutor, Patrick Fitzgerald.

The vice president “is very smart and very quick, but so is Fitz,” Mr. Tobias said.

Still, the decision not to put Mr. Cheney or Mr. Libby on the stand carries risks for the defense. One is that some issues raised by the defense may never be fully fleshed out for the jury.

In his opening argument, Mr. Wells stunned many in the courtroom by asserting that Mr. Libby was the victim of an effort to protect President Bush’s top political adviser, Karl Rove, who was a source for two of the first news accounts to identify Ms. Plame. Jurors saw some support for the claim in the form of a somewhat cryptic note in which Mr. Cheney vowed “not to protect one staffer and sacrifice the guy that was asked to stick his neck in the meat grinder.”

However, jurors have heard little testimony to explain the alleged scheme against Mr. Libby. Now, it seems jurors will hear neither Mr. Libby nor Mr. Cheney explain the note or its significance.

A former U.S. attorney for the capital, Roscoe Howard, said those kinds of openings could pose trouble for Mr. Wells.

“If he doesn’t bring together some of those loose ends, Pat’s going to have a field day,” Mr. Howard said.

In lieu, to some extent, of Mr. Libby, the defense yesterday called his former deputy, John Hannah, who said his boss sometimes had memory issues. “On certain things, Scooter just had an awful memory,” Mr. Hannah said. He said that “too many times to count” Mr. Libby repeated back ideas Mr. Hannah had given to him earlier in the day, apparently having forgotten that his deputy started the ball rolling.

Mr. Hannah also testified that at the time Ms. Plame’s identity allegedly was discussed at the White House his boss had a “very heavy” workload monitoring terrorist threats against America and reacting to crises in Iraq, Iran, North Korea, and Liberia.

While the defense noted repeatedly yesterday that terrorism and foreign policy issues were only half of Mr. Libby’s portfolio, his lawyers showed no interest in exploring the domestic agenda being pursued by Mr. Cheney’s team. Defense attorneys could have been concerned that the jury, which hails from the largely liberal capital, might have a negative reaction to discussions about privatizing Social Security or expanding domestic surveillance.

After about 90 minutes of defense questioning of Mr. Hannah, Mr. Fitzgerald mounted a terse six-minute counterattack. He noted that during a week Mr. Hannah said Mr. Libby was under a particular crush of vital business, Mr. Libby took an hour or two to meet with a reporter for the New York Times, Judith Miller, about issues that allegedly included some of the accusations being made by Mr. Wilson. Mr. Hannah conceded that only on a very important matter would he have gotten that kind of time from Mr. Libby.

Mr. Fitzgerald also elicited from Mr. Hannah that one of Mr. Libby’s duties was to “push back” against unfounded criticism of the vice president and that Mr. Libby was well-informed about the facts relating to Mr. Wilson’s claims.

Jurors also heard yesterday from the managing editor of the New York Times, Jill Abramson, who undercut Ms. Miller’s testimony that she suggested to Ms. Abramson that the Times pursue a story about Mr. Wilson’s wife.

“I have no recollection of such a conversation,” Ms. Abramson said. Judge Walton rejected a defense bid to question an NBC reporter, Andrea Mitchell, about comments she made on television in October 2003 suggesting that Ms. Plame’s identity was “widely known” among Washington reporters before it was published. Ms. Mitchell has since disavowed the statement, claiming that she misspoke or misunderstood the question.

Judge Walton said legal precedents precluded Ms. Mitchell’s testimony on that point because her earlier statement was hearsay and her current denial of advance knowledge about Ms. Plame was of no benefit to Mr. Libby’s defense.