WASHINGTON — Republicans moved yesterday to shut off debate on the nomination of Priscilla Owen to the 5th U.S. Circuit Court of Appeals, forcing a confrontation over the use of filibusters against judicial nominees expected to occur Tuesday unless a bipartisan group of senators can craft a compromise to defuse the dispute.

Sen. John Cornyn, R-Texas, acting on behalf of Senate Majority Leader Bill Frist, R-Tenn., filed the cloture motion at 2:20 p.m. after more than 24 hours of debate on Owen. Debate will continue Monday, with the cloture vote scheduled for Tuesday. A filibuster is the traditional delaying tactic of lengthy speeches by members of the minority party to block action in the Senate.

Frist's office said in a statement that, if Republicans fail to muster the 60 votes needed to end debate, as is likely, he will invoke the "nuclear option": a point of order designed to change Senate precedent to allow a simple majority to halt debate on judicial nominees and so named because Democrats vow to disrupt the Senate's work if Frist prevails.

With Supreme Court vacancies perhaps on the near horizon, the stakes are huge. If Republicans prevail, they will have an easier time confirming judges who, for example, think abortion rights are too permissive and church-state separation too restrictive.

Neither Frist nor Senate Minority Leader Harry Reid, D-Nev., is certain who has the votes to prevail if the nuclear option is invoked, according to both parties.

Reid told a group of columnists that he needed two votes to prevail in a showdown, indicating that four Republicans have agreed to side with Democrats. Separately, Republicans said fresh polling indicated the debate over judges has coincided with a dip in their approval ratings but a larger decline in Democratic support. Even so, only 37 percent of those surveyed support the change in Senate procedures, with 50 percent opposed, according to officials.

Nor is it clear whether the so-called Gang of 12 senators involved in negotiations can strike a deal in time to avert the clash on the Senate floor. Negotiators broke Thursday night, and many scattered for the weekend. Informal discussions continued yesterday and may take place today and tomorrow, but no face-to-face discussions are expected until Monday.

The group remained at an impasse over the circumstances under which Democrats in the group might use the filibuster in future fights over judicial nominations and whether Republicans in the group will forswear support for the nuclear option for the rest of the 109th Congress.

Sen. Joe Lieberman, D-Conn., one of those seeking a compromise, offered an insight during a speech on the Senate floor into why the talks have been so difficult. Lieberman said he hoped a compromise could be found.

But he argued passionately to preserve the right to filibuster a judicial nominee he believes is not qualified and said it is essential that judicial nominees be able to muster votes from more than one party. "That's what's on the line here," he said. "The institutional requirements of 60 votes is one of the last best hopes of bipartisanship and moderation."

Senate Judiciary Committee Chairman Arlen Specter, R-Pa., in a floor speech, decried the groups' activities. "One group is shouting to the Democrats, 'Filibuster forever,' " he said. "The other side is shouting to the Republicans, 'Pull the trigger.' ... What I think needs to be done is the issue ought to be returned to the Senate."

Meanwhile, Sen. Rick Santorum, R-Pa., issued an apology for remarks on the Senate floor the previous day in which he invoked the name of Nazi dictator Adolf Hitler in criticizing Democrats. "Referencing Hitler was meant to dramatize the principle of an argument, not to characterize my Democratic colleagues," Santorum said in a statement. "It was a mistake, and I meant no offense."

Reid's remarks to columnists and GOP polling data were provided by The Associated Press; Santorum's apology was reported by the Los Angeles Times.