WASHINGTON – Reports that President Bush’s top political adviser, Karl Rove, may have had a role in leaking the identity of an undercover CIA operative set off a feeding frenzy among the White House press corps yesterday and prompted sharp criticism from Democrats, including calls for Mr. Rove’s firing.

At a contentious briefing, journalists pummeled the unyielding White House press secretary, Scott McClellan, with questions about why he once said Mr. Rove had no role in the leak of Valerie Plame’s identity. Reporters also demanded to know if Mr. Bush would follow through on his pledge to fire any staffer who may have been involved. The spokesman turned aside all the questions, saying that the White House had been asked not to comment by prosecutors investigating the matter.

“The president directed the White House to cooperate fully with the investigation, and as part of cooperating fully with the investigation, we made a decision that we weren’t going to comment on it while it is ongoing,” Mr. McClellan said.

During the tense, 31-minute exchange, the press secretary ducked more than 30 questions on the subject, including queries about whether Mr. Bush continues to have confidence in Mr. Rove and about whether the political aide, who was elevated to the position of deputy chief of staff earlier this year, has seen his portfolio curtailed.

The beleaguered White House spokesman appeared to concede that the disclosures had raised doubts about his veracity. Reporters “know the type of person that I am,” Mr. McClellan said defensively. “I will be glad to talk about this at the appropriate time, and that’s once the investigation is complete.”

On Capitol Hill, Democrats launched salvo after salvo at Mr. Rove, accusing him of a grave breach of trust.

In e-mail to supporters, Senator Kerry of Massachusetts repeated his calls for Mr. Rove’s dismissal. “There appears to be no limit to the lengths to which Rove – and this Administration – will go,” Mr. Kerry wrote as he solicited signatures for a petition aimed at forcing Mr. Rove out.

Senator Lautenberg of New Jersey urged that Mr. Rove’s security clearance be revoked.

And Senator Schumer sent Mr. Rove a letter urging him to “clear the air” about the alleged leak, which many Democrats believe was intended to retaliate against Ms. Plame’s husband, Joseph Wilson IV, a former diplomat who publicly tilted with Mr. Bush over Iraq.

The sudden barrage of questions from the White House press corps came after bloggers pointed out that journalists neglected at least four opportunities to question Mr. McClellan about the episode last week, after reports of Mr. Rove’s role began to emerge.

On Sunday, Newsweek reported that that it obtained an e-mail in which a Time magazine correspondent subpoenaed in the case, Matthew Cooper, described a confidential conversation with Mr. Rove. According to the e-mail, the Bush confidant mentioned Ms. Plame’s CIA connection, though apparently without using her name or making reference to her undercover status.

If Mr. Rove did not know that Mr. Wilson’s wife was a covert agent, it would be difficult for prosecutors to bring criminal charges against him, legal analysts said.

Ms. Plame’s name and her CIA connection were first noted publicly in a July 2003 syndicated column written by Robert Novak. The disclosure resulted in a criminal investigation headed by a special prosecutor, Patrick Fitzgerald. He sought testimony from several prominent Washington reporters. Mr. Novak has declined to explain whether he identified his sources to the grand jury, but he said he will offer more details when the probe concludes.

Another journalist, Judith Miller, is in a Virginia jail after refusing to discuss her reporting on the story.

The Time magazine reporter whose notes reportedly finger Mr. Rove as a source, Matthew Cooper, narrowly avoided jail last week after he said his source released him from a confidentiality pledge. However, the details of that release remain murky. Mr. Rove’s attorney led reporters to believe that Mr. Rove was not a confidential source on the story. The lawyer later issued a narrow denial, saying that Mr. Rove never discussed Ms. Plame’s name with any reporter.