WASHINGTON -- As another Republican called for his resignation, Attorney General Alberto Gonzales told a skeptical Senate panel Thursday that he didn't know why two federal prosecutors were being fired when he abruptly dismissed them, and he admitted he never reviewed evaluations for any of the eight U.S. attorneys fired last year.

In a day-long hearing punctuated by combative exchanges, Senate Judiciary Committee members from both parties openly questioned whether Gonzales should remain. The attorney general conceded that he couldn't remember exactly when he fired the prosecutors. The dismissals in June and December touched off a firestorm that now imperils his position.

Sen. Tom Coburn, R-Okla., a Judiciary member, said Gonzales should step down. "Confidence in U.S. attorneys has been undermined, and the reputation of the attorney general's office has been tarnished," he said. "To me, there has to be consequences. The best way to put this thing behind us is your resignation."

Coburn is the third GOP senator to urge the attorney general to resign, following John Sununu of New Hampshire and Gordon Smith of Oregon.

Sen. Arlen Specter of Pennsylvania, the panel's top Republican, said Gonzales' testimony had not repaired "a loss of credibility." He stopped short of calling for the attorney general's resignation, saying that was up to Gonzales and President Bush.

Gonzales admitted that the process for removing the prosecutors was "flawed" but continued to assert that "nothing improper occurred." And despite many "mistakes," Gonzales said he still believes the firings were justified.

"I have learned important lessons from this experience, which will guide me in my important responsibilities," Gonzales said. "I believe that Americans focus less on whether someone makes a mistake than on what he or she does to set things right."

Bush was "pleased" with Gonzales' testimony, White House spokeswoman Dana Perino said. The attorney general had the president's "full support," she said.

Gonzales has been the focus of intense scrutiny since the eight U.S. attorneys were fired, largely because of shifting and contradictory explanations for the dismissals that have been given by him, his top aides at the Justice Department and White House officials.

The attorney general's appearance on Capitol Hill came less than a month after his former chief of staff Kyle Sampson contradicted Gonzales' prior public statements on the issue.

The Judiciary Committee is investigating whether the firings were motivated by partisan politics or as retaliation for the prosecutors' choices of investigative targets. Gonzales' appearance has been widely viewed by Democrats and Republicans as a make-or-break moment for him.

Some of the harshest questioning Thursday came from Republicans.

At one point, Sen. Lindsey Graham, R-S.C., said he was convinced that department officials "made up reasons" to fire the prosecutors because of personality clashes and other differences.

Gonzales challenged Graham's assertion, but the senator pressed on. "Is it fair to say that these people (the prosecutors) were not the right people at the right time?" Graham asked.

"I think that's a fair statement," Gonzales responded.

"If I applied that same standard to you, what would you say?" Graham asked. Gonzales responded, "I believe that I continue to be effective as the attorney general of the United States."

The exchange set off murmurs in the packed hearing room, as Gonzales defended his leadership. He acknowledged missteps and said he knew "what I would do differently."

Senators repeatedly homed in on Gonzales' admitted mistakes, with the attorney general responding with a sometimes lawyerly defense of his actions.

Committee Chairman Patrick Leahy, D-Vt., set the tone in the morning when he suggested that the Justice Department "seems to have lost its way" and is "experiencing a crisis of leadership" unlike others in its 137-year history.

"The Department of Justice must not be reduced to another political arm of the White House," he said.

Leahy spent part of the day quieting more than a dozen demonstrators, some dressed in orange jumpsuits to mock Gonzales' previous role in formulating policy on the treatment of terrorism suspects when he was White House counsel.

"Liar!" Desiree Fairooz, 50, shouted during a break in the attorney general's testimony. Fairooz came dressed in a flowing pink robe, flip-flops and matching sash identifying her as "Lady Justice."

Some, including Adam Kokesa, 25, were keeping a running count of how often Gonzales said he didn't remember or couldn't recall in response to senators' questions. By lunchtime, Kokesa said, the number had reached nearly 40.

At the end of the day, Sen. Charles Schumer, D-N.Y., renewed his call for Gonzales' resignation.

Schumer said Gonzales, despite weeks of preparation, demonstrated a lack of knowledge about the workings of his own department. By his own count, Schumer said, Gonzales answered that he didn't know or couldn't recall to about 100 questions.

"I urge you," Schumer said, "for the good of the department, for the good of the country, step down."

Specter, meanwhile, was blunt and said Gonzales' credibility and job were at stake. "You come to this hearing with a heavy burden of proof ... to justify the replacement of these U.S. attorneys and to demonstrate that you can provide the leadership of the Department of Justice," Specter said.

Specter took issue with Gonzales' statements at a news conference last month that he was not involved in any discussions about the removals prior to his decision to fire the eight prosecutors

The line of questioning produced a sharp exchange when Gonzales quipped that he always prepares for his hearings before the Senate.

An angry Specter shot back, "Did you prepare for your press conferences? Were you prepared for the press conference where you said there weren't any discussions involving you?"