WASHINGTON – The Senate opened a fiery debate yesterday over one of President Bush’s contentious judicial nominees, kicking off a partisan showdown that could result in the end of the minority party’s ability to filibuster judicial nominations.

Democrats have denounced Justice Priscilla Owen as an extremist whose ideas lay on the fringe of the otherwise conservative Texas Supreme Court. The justice, whom President Bush nominated to the 5th U.S. Court of Appeals, has waited four years for senators to vote on her nomination and has become a symbol of the minority’s ability to continually block judges.

“I do not rise for party. I rise for principle,” the Senate Republican leader, Senator Frist of Tennessee, said yesterday as he launched the long-awaited debate. “I rise for the principle that judicial nominees with the support of a majority of senators deserve up-or-down votes on this floor.”

He called on senators to “confirm the nominee. Reject the nominee. But, in the end, vote.”

Republicans are expected to allow the debate to continue for several days before imposing the rule change known as the “nuclear option” or the “constitutional option,” which would effectively end senators’ ability to endlessly hold up votes on federal judicial nominees.

Currently, 60 votes are necessary to end a filibuster, but only a simple majority is necessary to confirm a judge. Without the ability to filibuster, Mr. Bush’s nominees will most likely sail through a vote. There are currently 55 Republicans, 44 Democrats, and one Independent in the Senate.

During the floor debate yesterday, Senator Schumer accused Republicans of throwing a “temper tantrum” and of “blowing up the Senate … all because 10 judges haven’t been approved.” “The reason the majority leader hasn’t called a vote is the courageous handful who have resisted the pressure,” Mr. Schumer said of Republican senators.

Mr. Schumer confronted Mr. Frist, asking him whether despite his current misgivings about the tactic, he had voted in 2000 to uphold a filibuster of a Clinton nominee to the 9th Circuit, Judge Richard Paez.

Mr. Frist did not answer the question directly. He stressed that Democrats had used the filibuster “in a routine way” to keep the judges off the bench.

“The issue is not cloture votes, per se. It’s the partisan, leadership-led use of cloture vote to kill, to defeat, to assassinate these nominees,” Mr. Frist said.

The Democratic leader, Senator Reid of Nevada, defended the filibuster as “a part of the fabric of this institution” and “an integral part of our country’s 217 years of history.”

He accused Republicans of wanting to change the very nature of the Senate – where the minority is traditionally more powerful than in the House – in the pursuit of “absolute power.”

“The right to extended debate is never more important than when one party controls Congress and the White House,” Mr. Reid said. “Right now, the only check on President Bush is the Democrats’ ability to voice their concern in the Senate,” he said.

The two leaders broke off negotiations over a solution last week.

Several senators continued to propose last-minute compromises yesterday, but the partisan climate did not appear to favor a quick fix. Mr. Frist had proposed ending the filibuster in exchange for ending the ability of senators to block nominees in committee – as was the Republican practice under President Clinton.

The chairman of the Judiciary Committee, Senator Specter, a Republican of Pennsylvania, yesterday proposed allowing senators to vote on judges according to their personal conscience, rather than along party lines.

In a flurry of closed-door meetings, a handful of other senators from both parties discussed the possibility of trading Democratic support for some judges in exchange for the Republican withdrawal of others.

But dedicated opponents of the filibuster predicted the negotiations would not succeed.

“Senator Frist is resolute. Republicans are resolute, and any deal that is not based on principle would be unacceptable to the Republican base, and would be presumably unacceptable to the Democratic base. I think the map is charted,” said a former aide to Mr. Frist, Manuel Miranda, who now coordinates anti-filibuster efforts of outside groups through the National Coalition to End Judicial Filibusters.

Yesterday, Republicans were said to be debating whether to push for an end to debate at the end of the week, or to continue until Monday or Tuesday in an effort to make their case on the multitude of political talk shows that air on Sunday.

Much of yesterday’s Senate debate centered on the qualifications of Justice Owen.

Democrats emphasized that the judge had frequently broken ranks with other conservatives on the Texas court to rule against plaintiffs in favor of corporations, and that she had attempted to gut a Texas law that allowed some minors to ask a judge for an exemption to a requirement that they notify their parents before having an abortion.

Several Democratic senators noted that the attorney general, Alberto Gonzales, then a colleague on the Texas bench, had disagreed with her views in several cases.

“Not once, not twice, but numerous times, Justice Gonzales and his other colleagues on the Texas Supreme Court have noted that Priscilla Owen ignores the law to reach her desired result,” said Senator Kennedy, a Democrat of Massachusetts. Republicans countered that Mr. Gonzales supports her nomination. They also stressed that she was re-elected to the Texas court with 84% in 2000.

“How can anyone try to say she is out of the mainstream?” asked Senator Chambliss, a Republican of Georgia.