WASHINGTON — Senator Specter said the threat of a “very substantial” no-confidence vote in the Senate may force Attorney General Gonzales to resign before lawmakers cast their ballots.

Mr. Specter, 77, the ranking Republican on the Judiciary Committee, said more Republicans may join the majority Democrats in favor of a resolution expressing a lack of confidence in Mr. Gonzales over the way he handled the firing of eight federal prosecutors.

“You already have six Republicans calling for his resignation,” Mr. Specter, of Pennsylvania, said on CBS’s “Face the Nation” program. “I have a sense,” he said, “that before the vote is taken, that Attorney General Gonzales may step down.”

Democratic Senators Schumer of New York and Feinstein of California said the full Senate may vote on their resolution this week. While a largely symbolic gesture, such a measure would add to the political pressure on Mr. Gonzales, 51, a longtime adviser to President Bush who the president appointed as attorney general in 2005.

“The bottom line is the only person who thinks that the attorney general should remain attorney general is the president,” Mr. Schumer, 56, said yesterday on “Fox News Sunday.” “The president can keep him. He has the constitutional power to do it. But we have the constitutional power to try to pressure the president to understand that Gonzales is no good.”

The Senate and House Judiciary committees are trying to determine whether Mr. Gonzales fired the U.S. attorneys to interfere with criminal investigations. Lawmakers expanded their probe after testimony last week by a former top Justice Department official who said Mr. Gonzales, when he was White House counsel, pressured a hospitalized Attorney General Ashcroft to approve a secret spying program in 2004.

Mr. Specter last week called the Justice Department “close to being dysfunctional,” and said Mr. Gonzales seems “unable to perform” his duties as America’s chief law enforcement officer.