WASHINGTON — Senators of both parties challenged Attorney General Gonzales’s candor about the firing of eight U.S. attorneys and questioned his fitness to remain in office.

Members of the Senate Judiciary Committee subjected Mr. Gonzales to a rapid-fire barrage of questions that demanded detailed explanations of the firings and his role in them. The controversy has triggered calls from lawmakers in both parties for his removal. President Bush has stood by Mr. Gonzales, saying he has confidence in him.

“We have to evaluate whether you are really being forthright,” said Pennsylvania’s Senator Specter, the panel’s top Republican. “Your characterization of your participation is significantly, if not totally, at variance with the facts.”

Mr. Gonzales said he couldn’t remember when he approved the firings and conceded that he relied almost solely on the advice of top Justice Department officials who reviewed the performance of U.S. attorneys. Nor could he recall a November 27 meeting where other Justice Department officials say the plan was approved, the attorney general said.

“How can you be sure you made the decision?” said Senator Leahy, the Vermont Democrat who heads the panel.

House and Senate panels are investigating whether the U.S. attorneys were dismissed for improper political reasons. Yesterday, the attorney general stood by his decisions. Still, Mr. Gonzales conceded that “those eight attorneys deserved better” treatment from him and the Justice Department.

Senator Coburn, a Republican of Oklahoma, facing Mr. Gonzales across the hearing room, demanded his resignation. “The best way to put this behind us is your resignation,” he said. The firings were handled incompetently, and “there has to be consequences to accepting responsibility” for those mistakes, he told Mr. Gonzales.

“I don’t know whether or not that puts everything behind us,” Mr. Gonzales replied. “I know the mistakes that were made here, and I am committed to fix those mistakes.”

In one of the sharpest exchanges at yesterday’s hearing in Washington, Mr. Specter scolded the attorney general for interjecting that he is always prepared for his appearances before the Judiciary Committee.

“Do you prepare for your press conferences?” Mr. Specter shot back. “And were you prepared when you said you weren’t involved in any deliberations” on the firings?

Mr. Gonzales, at a March 13 news conference, said he hadn’t attended meetings or read memos about the dismissals. Documents given to Congress showed he attended the November 27 meeting, which took place 10 days before the dismissals.

“I’ve already conceded that I misspoke at the press conference,” Mr. Gonzales said.

Mr. Specter also questioned Mr. Gonzales’s continued assertion that he had only “limited involvement in the process” of replacing the prosecutors. That was contradicted by the testimony of top Justice Department officials, Mr. Specter said.

Republican senators joined Democrats in questioning statements by Justice Department officials that the prosecutors were dismissed for poor performance.

“Most of this is a stretch,” Senator Graham, a Republican of South Carolina, told Mr. Gonzales. “It’s clear to me that some of these people just had personality conflicts” with Bush administration officials, and the Justice Department “made up reasons to fire them.”

Mr. Graham noted that Mr. Gonzales had once explained that the decision “just came down to these were not the right people at the right time.”

“If I applied that standard to you, what would you say?” Mr. Graham said.

“I believe that I continue to be effective as the attorney general,” Mr. Gonzales replied. “I acknowledge the mistakes that I have made here.”

Alabama’s Senator Sessions said he found “troubling” Mr. Gonzales’s inability to remember the November 27 meeting.

“There are some very serious problems, Mr. Attorney General,” said Mr. Sessions. “Your ability to lead the Department of Justice is in question.”

Mr. Sessions said Mr. Gonzales “should have said no” to recommendations the prosecutors be fired. “I do not believe this was a necessary process,” said Mr. Sessions, a former U.S. attorney.

Mr. Gonzales said he assigned his chief of staff, D. Kyle Sampson, to assemble recommendations from top Justice Department officials about which U.S. attorneys would be replaced. Mr. Sampson, who resigned last month, has disputed Mr. Gonzales’s description of his own role, as have Associate Attorney General William Mercer and Michael Battle, former liaison to U.S. attorneys, Mr. Specter said.

By insisting that he didn’t participate in discussions to pick candidates for firing, the attorney general was “carrying forward this same pattern of not being candid,” Mr. Specter told Mr. Gonzales during questioning that resembled cross-examination during a trial.

Mr. Specter, himself a former prosecutor, quoted statements by Messrs. Sampson, Mercer, and Battle that Mr. Gonzales attended meetings where the dismissals were discussed at length.

These included a June 2006 meeting to weigh the possible dismissal of Carol Lam, the U.S. attorney in San Diego, Mr. Specter said.

Mr. Sampson also told investigators that Mr. Gonzales was consulted about removing H.E. “Bud” Cummins III, the U.S. attorney in Little Rock, Ark., who was replaced by an ex-aide to Karl Rove, Mr. Bush’s top political adviser.

“Do you say it’s a fair, honest characterization to say you had only a limited involvement in the process?” Mr. Specter asked.

“I don’t want to quarrel with you,” Mr. Gonzales replied. “I had knowledge there was a process going on.” He said he didn’t view discussions about Mr. Lam’s performance as part of Sampson’s “project” to identify prosecutors for replacement.

“Were you involved in the process? Were you involved to a limited extent only?” Mr. Specter said.

Mr. Specter compared yesterday’s session to a confirmation hearing. “You come to this hearing with a heavy burden of proof, to reestablish your credibility, to justify the replacement of these U.S. attorneys and to demonstrate that you can provide the leadership of the Department of Justice,” he said.

Mr. Gonzales accused Democrats of attacking career Justice Department prosecutors by questioning whether politics formed the basis of some decisions to bring criminal prosecutions.

“When you attack the department for being partisan, you’re really attacking the career professionals,” the attorney general said. “That’s not right.”

“Your conduct of this department has made it more difficult for these professionals to do their job effectively,” Senator Durbin, a Democrat of Illinois, told Mr. Gonzales.

Mr. Gonzales confirmed that Mr. Rove late last year relayed complaints that three U.S. attorneys weren’t vigorously prosecuting voter fraud. One of those mentioned by Mr. Rove was David Iglesias, the U.S. attorney in New Mexico who was fired in December. Mr. Sampson has said Mr. Gonzales told him about the conversation in October.

The attorney general said he couldn’t recall a conversation with the president about the same complaints, which the White House said took place sometime in October.

“There was a meeting in October in which the president, as I understand it, relayed to me similar concerns,” Mr. Gonzales said, citing an October 11 calendar entry showing he had gone to the White House that day to meet with Mr. Bush.

Mr. Gonzales said he couldn’t recall whether Mr. Iglesias’s name was added to the list of prosecutors to be fired before or after the November 7 election.

He said he had been aware of complaints that Mr. Iglesias was not aggressive enough in pursuing public corruption as early as November 2005. That’s when Pete Domenici, New Mexico’s Republican senator, complained to him that Mr. Iglesias was “in over his head,” Mr. Gonzales said.