WASHINGTON -- Some Democratic senators said yesterday that they were prepared to filibuster a Supreme Court nominee they find unacceptable, and urged President Bush to name a ''mainstream conservative" to replace retiring Justice Sandra Day O'Connor.
Lawmakers in both major parties appealed for calm and reason as interest groups gear up for what is expected to be a bruising and expensive battle. But both camps said they were prepared for a fight, with Republicans demanding an up-or-down vote on Bush's eventual nominee and Democrats holding out the possibility they may mount a filibuster if they can't accept the president's selection.
''It's really up to the president, whether we're going to have someone that is a consensus candidate, someone that can bring the country together, someone that can rally the Republicans and Democrats," Senator Edward M. Kennedy said yesterday on ABC's ''This Week."
''We want to be able to support [the president], but if he wants to have a fight about it, then that's going to be the case," Kennedy said.
Two other Democratic senators, Joseph R. Biden Jr. of Delaware and Patrick Leahy of Vermont, said yesterday that they hoped a filibuster could be avoided, but would not rule out the option.
Conservatives are clamoring for a justice they say represents their values -- antiabortion, opposed to gay marriage, and in favor of religious expression in public places. Many have already come out against the potential nomination of Attorney General Alberto Gonzales because they question his antiabortion credentials.
But two key Republicans on the Senate Judiciary Committee, which considers judicial nominations, yesterday pointedly refused to criticize Gonzales and signaled that they were not pushing an ultraright nominee to the Supreme Court.
The chairman of the Senate Judiciary Committee, Arlen Specter, a moderate Pennsylvania Republican, suggested he would be concerned about a nominee who believed categorically in ''original intent" -- meaning a strict interpretation of the Constitution based on what the founders intended more than 200 years ago.
Specter, also speaking on ''This Week," brought up the case of Robert Bork, a Supreme Court nominee who was not confirmed amid questions about his commitment to civil rights.
He said Bork has come up repeatedly as someone who believes in original intent. ''If you followed original intent," Specter said, ''the galleries in the United States Senate would still be segregated, with Caucasians on one side and African-Americans on the other side."
Senator Orrin G. Hatch, a conservative Utah Republican, said Bush had every right to appoint a conservative nominee, as the president indicated he would do in both of his presidential campaigns. But Hatch also spoke highly of Gonzales, whom cultural conservatives oppose.
Gonzales ''is a terrific human being, a good lawyer . . . a person who can handle the job. If the president chooses Alberto Gonzales . . . I think we would all feel pretty good about it," Hatch said on CBS's ''Face the Nation." ''If he gets picked, I'm certainly going to support" him, Hatch said.
Bush was at Camp David yesterday, considering his options, and is not expected to make an announcement until next week at the earliest. Specter said he was open to holding hearings in September, but said there was talk of having them in August, when Congress is usually in recess.
Gonzales was on a surprise trip to Iraq yesterday.
Specter, whose rise to the Judiciary Committee chairmanship was opposed by conservative activists because they feared he would not be a strong antiabortion voice, also suggested the current opening might be considered differently because the nominee would replace Sandra Day O'Connor instead of Chief Justice William H. Rehnquist.
O'Connor was a Republican appointee who has turned out to be a swing vote on the high court; Rehnquist was a reliable conservative vote on the court.
''I think that there are different considerations," Specter said. ''There's the gender factor -- should he appoint another woman? So, it's a different approach, and I think the president will factor that in."
Specter, an irascible, veteran lawmaker and former prosecutor, has frequently sparred with members of his own party, especially those in the GOP's conservative wing.
Specter gave no sign yesterday that there is a specific nominee he would oppose, but his remarks indicated he would not participate in a conservative activists' campaign to send a very conservative nominee to the high court.
Bork disputed Specter's characterization of his views on race. ''I know Specter, and the truth is not in him," Bork said on CNN's ''Late Edition." Bush should not select a so-called compromise candidate to ease high tension on Capitol Hill, Bork added.
''His duty is to find somebody who will make a fine judge, not someone who is a compromise candidate with Teddy Kennedy," said Bork, whom Kennedy opposed sending to the high court.
Jan LaRue, chief counsel for Concerned Women for America, echoed the words of many fellow conservatives in insisting that Bush pick a justice who is a known conservative. She and other activists said they were very disappointed in two Republican picks, O'Connor and David H. Souter, who have not been solid conservative votes.
''This is why a president shouldn't select someone based on sex or race, but should look very seriously at their opinions, their speeches, and other writings to make sure they do, in fact, fit the profile of an [Antonin] Scalia or a [Clarence] Thomas," LaRue said, referring to two justices Bush has said are his favorites on the Supreme Court.
Six weeks ago, seven Democratic and seven Republican senators forged a deal that broke a stalemate over confirmation of Bush's court nominees, agreeing to filibuster them only in ''extraordinary circumstances." Senator Lindsey Graham of South Carolina, one of the seven Republicans, said yesterday that disagreement with a nominee's legal views would not constitute extraordinary circumstances.