WASHINGTON -- Senate Republicans set the stage for a showdown Tuesday over the filibusters blocking several of President Bush's judicial nominees, a historic vote that could determine whether an out-of-power party can stop a president from placing like-minded jurists on the nation's highest courts.

Unless compromise-minded centrists can strike a deal before then, Senate Majority Leader Bill Frist will force a test vote Tuesday on Texas judge Priscilla Owen's nomination to the 5th U.S. Circuit Court of Appeals.

Under the expected chain of events set in motion Friday: If the nomination doesn't garner 60 votes -- the threshold for overcoming a filibuster -- Frist then will have the presiding officer, expected to be Vice President Dick Cheney in his role as Senate president, declare that filibusters are illegal for Supreme Court and federal appellate court nominees.

The Republican majority presumably then would uphold that ruling, a procedure that has become known as the "nuclear option" because senators say it would blow up relations between the two parties.

"The Senate clock centered above the vice president's chair is in a countdown, second by second, to the appointed hour and minute when a nuclear explosion may render the Senate inoperative, or at least do substantial damage to this institution," said Judiciary chairman Arlen Specter, R-Pa.

GOP Sen. John Cornyn, a former judge who served with Owen on the Texas Supreme Court, started the countdown Friday by demanding a vote on her nomination. When Democratic leader Harry Reid blocked that vote, Cornyn called for the Tuesday test vote that would lead to a decision on the filibusters of all seven of Bush's blocked judicial nominees.

"If we were just permitted to cast a vote, a bipartisan majority would confirm these nominees today," Cornyn said. "This really amounts to a veto. A partisan minority has attempted to cast a veto of majority rights, bipartisan majority rights."

Democrats argue that they are within their rights to filibuster judicial nominees and that Republicans are overstepping the bounds by trying to stop them. They threaten to block the president's legislative agenda if Frist is successful at eliminating judicial filibusters.

"This extralegal changing of the Senate rules will cause a permanent tear in the Senate fabric because it violates a deeply held American value -- playing by the rules," said Sen. Carl Levin, D-Mich.

While it takes 60 votes to overcome a filibuster, Republicans intend to supersede the rule by a simple majority vote. With 55 seats, Republicans could afford five defections if all 100 members vote and still prevail on the strength of Cheney's ability to break ties.

Reid told a group of columnists during the day he was within two votes of having the strength to prevail in a showdown, indicating that four Republicans have agreed to break ranks and side with the Democrats.

Separately, Republicans said they had received fresh polling that 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 supports the change in Senate procedures, with 50 percent opposed, according to officials familiar with the survey.

Senate centrists are trying to avert Tuesday's showdown, but three days of backroom negotiations have yet to produce a deal in which six Republicans and six Democrats are willing to block Frist from banning filibusters and block Reid from filibustering all of Bush's controversial nominees.

While negotiators aren't expected to meet again before Monday evening, senators said they would try to talk by telephone over the weekend to move things along because of the impending Tuesday deadline.

The Senate tentatively is expected to remain in session throughout the night on Monday. Democrats made plans to show in a side room "Mr. Smith Goes to Washington," the classic 1939 film in which Jimmy Stewart's character stages a 24-hour filibuster.

Negotiators are hoping to craft a deal that would allow some nominees to be confirmed while leaving others behind. One plan would allow final votes on Owen, California Supreme Court Justice Janice Rogers Brown and former Alabama Attorney General William H. Pryor, as well as Michigan nominees Susan Neilson, Richard Griffin and David McKeague. The nominations of William G. Myers and Henry Saad would remain stuck.

Another would confirm all of the previous nominees except Saad, White House staff secretary Brett Kavanaugh and Pentagon lawyer William Haynes. Kavanaugh's nomination to the D.C. circuit and Haynes' to the 4th U.S. Circuit of Appeals are recent additions to the negotiations.

Another part would have Democrats signing a compromise document pledging their "good faith" not to filibuster future nominees except in extraordinary circumstances. If they uphold "the spirit and commitment," Republicans would "commit to oppose the rules changes" sought by Frist.

Senior Sens. John Warner, R-Va., and Robert Byrd, D-W.Va., also working on language to set up a Senate-selected pool of court candidate from which the president can choose if he wants to ensure confirmation. Their goal "is to arrive at a process that will permit the Senate to move forward this Congress with its important business, while establishing a workable blueprint for the Senates present and future consideration of judicial nominees," Warner said Friday.

Democrats have prevented final votes on 10 of Bush's first-term appeals court nominees and have threatened to do the same this year to seven the president has renominated, including Owen and Brown. The Senate has approved 208 Bush judicial nominees, including 35 appeals court judges.