Washington ? Die-hard Democratic critics of Supreme Court nominee Samuel Alito threatened Thursday to block a vote on his confirmation, and Republicans countered with a move designed to force his approval by early next week.

“It is time to establish an end point” in the debate over President Bush’s selection to replace Justice Sandra Day O’Connor, said Senate Majority Leader Bill Frist, R-Tenn.

Sen. Edward M. Kennedy, D-Mass., said he and other Democrats had refused to agree to a timetable for ending debate. “There’s some division in our caucus,” he conceded.

Democratic Leader Harry Reid signaled as much in remarks on the Senate floor. He offered no support for Kennedy, John Kerry and others whose filibuster represents a last stand against Alito’s confirmation.

“There’s been adequate time for people to debate,” Reid said.

Alito, 55 and a 15-year veteran of the federal appeals court, has more than 50 votes for confirmation. He gained the support of Democrats Tim Johnson, of South Dakota, and Robert C. Byrd, of West Virginia, during the day, and has the backing of at least 52 of the Senate’s 55 Republicans.

The Senate will vote Monday on cutting off debate. If Alito’s supporters get 60 votes in the 100-member body, the confirmation vote will follow on Tuesday.

Frist said he had been unable to win a commitment from all senators on a time for a final vote. Instead, he set the stage for cutting off debate Monday with what is known as a cloture vote.

Democrats’ concern over Alito’s nomination has been heightened because he would replace O’Connor, who has been the swing vote on 5-4 rulings that maintained abortion rights, preserved affirmative action and limited the application of the death penalty.

Conservatives agree that Alito could push the court to the right, but they welcome the prospect.

President Bush earlier in the day called for the Senate to confirm his nominee.