WASHINGTON — Senator Sununu of New Hampshire yesterday became the first Republican in Congress to call for Attorney General Alberto Gonzales’s dismissal, hours after President Bush expressed confidence in his embattled Cabinet officer.

Mr. Gonzales has been fending off Democratic demands for his firing in the wake of disclosures surrounding the ousters of eight U.S. attorneys — dismissals Democrats have characterized as a politically motivated purge.

Support from many Republicans had been muted, but there was no outright GOP call for his dismissal until now.

“I think the president should replace him,” Mr. Sununu said in an interview with the Associated Press. “I think the attorney general should be fired.”

Mr. Bush, at a news conference in Mexico, told reporters when asked about the controversy: “Mistakes were made. And I’m frankly not happy about them.”

But the president expressed confidence in Mr. Gonzales, a longtime friend, and defended the firings. “What Al did and what the Justice Department did was appropriate,” he said.

What was “mishandled,” Mr. Bush said, was the Justice Department’s release of some but not all details of how the firings were carried out.

The developments unfolded as presidential aides labored to protect White House political director Karl Rove and a former counsel, Harriet Miers, from congressional subpoenas.

The White House dispatched presidential counsel Fred Fielding to Capitol Hill to negotiate the terms of any testimony by White House aides in an institutional tug-of-war reminiscent of the Watergate and the Iran-Contra scandals.

Mr. Sununu said the firings of the prosecutors, together with a report last Friday by the Justice Department’s inspector general criticizing the administration’s use of secret national security letters to obtain personal records in terrorism probes, shattered his confidence in Mr. Gonzales.

“We need to have a strong, credible attorney general that has the confidence of Congress and the American people,” said Mr. Sununu, who faces a tough re-election campaign next year. “Alberto Gonzales can’t fill that role.”

Some of the dismissed prosecutors complained at hearings last week that lawmakers tried to influence political corruption investigations. Several also said there had been Justice Department attempts to intimidate them.

E-mails between the Justice Department and the White House, released Tuesday, contradicted the administration’s earlier contention that Mr. Bush’s aides had only limited involvement in the firings.

Senator Reid, a Democrat of Nevada, predicted yesterday that Mr. Gonzales would soon be out.

“I think he is gone. I don’t think he’ll last long,” Mr. Reid said in an interview with Nevada reporters. Asked how long, Mr. Reid responded: “Days.”