ALBANY – Citing a recent bipartisan compromise on the treatment of judicial nominees, Senator Schumer said yesterday that Democrats on the Senate Judiciary Committee are prepared to use judicial philosophy as justification for thwarting any of President Bush’s nominees to replace Justice O’Connor.

The comments by New York’s senior senator raised the possibility that any nominee who is acceptable to most Republicans would be blocked by a filibuster in the Senate – the same situation that lawmakers had earlier avoided.

Democrats and Republicans agreed in May that nominees for federal judgeships would be held up only under “extraordinary circumstances” after Democrats threatened to filibuster three of Mr. Bush’s nominees. The deal allowed Democrats to maintain a say over future nominees and prevented Republicans from exercising a previously unused parliamentary option known as the “nuclear option” to break a filibuster with a simple majority.

Some Republicans viewed the compromise as too much of a concession to Democrats, since neither party defined what would constitute an extraordinary circumstance. Those concerns intensified last week when Justice O’Connor made the surprise announcement that she would step down from the high court at the end of the session.

If the nomination process gets ugly, as many expect it to, both the filibuster and the nuclear option may get put back on the table.

One member of the 14-person group that brokered the compromise on judicial nominees, Senator Graham, a Republican of South Carolina, said Sunday that disagreement with a nominee’s judicial philosophy does not constitute an extraordinary circumstance. He cited ethical lapses instead as legitimate reason for blocking a nominee.

“Ideological attacks are not an extraordinary circumstance,” Mr. Graham said on “Fox News Sunday.”

Yet Mr. Schumer, speaking to reporters at a press conference on another issue here yesterday, said a nominee’s judicial philosophy could indeed constitute an extraordinary circumstance and warrant obstruction.

The minority party has only attempted to filibuster a Supreme Court nominee once, in 1968, though neither party strongly supported the choice, Abe Fortas. A Democrat-controlled Senate rejected a Reagan nominee, Robert Bork, in 1988. Senators approved President Clinton’s two picks – Justices Stephen Breyer and Ruth Bader Ginsburg – 96-3 and 87-9, respectively.

“The bottom line is that the agreement said ‘extraordinary circumstances,’ but it also said the extraordinary circumstances are at the discretion of each of the individual senators,” said Mr. Schumer, who sits on the judiciary committee. “So you’d have to ask each of them, they signed it. But I’ve talked to some, and of course judicial philosophy could be within in the realm of extraordinary circumstances. For me, for sure, and I think for the people who signed the agreement, most of them.”

Mr. Bush has given no indication as to whom his nominee will be, but he has spoken admiringly in the past of Justices Scalia and Thomas. Mr. Schumer said yesterday he will not use a litmus test, even on the issue of abortion, to determine the legitimacy of a presidential nominee. Mr. Schumer, who opposes gay marriage, said a nominee’s position on that issue would also not influence his view of their legitimacy.

“The bottom line is that I don’t have any litmus test,” Mr. Schumer said. “Period.”

Mr. Schumer said his one overriding concern in reviewing Mr. Bush’s first nominee to the Supreme Court would be that he or she is disposed to interpret the Constitution rather than to “write new law.” He said only candidates who meet this standard would be considered legitimate. Mr. Schumer said he is resigned to the fact that Mr. Bush will nominate a conservative, but said an ideologue would create a fight.

As an example of two opposing “extremes,” Mr. Schumer cited a former justice, William Brennan, and Mr. Scalia, a Reagan appointee who was approved by the Senate by a vote of 98-0.

“It would be great if we could avoid a fight,” Mr. Schumer said. “And the president, look, make no mistake about it, he’s going to choose a conservative. But it could be a Sandra Day O’Connor type of conservative – thoughtful, mainstream, with the ability to see the other side. Or it could be a way off the chart ideologue, which would create a fight. … I don’t like ideologues on the bench. I’ve said I think a good court will have one Scalia and one Brennan. Not five of either one.”

Justice O’Connor’s announcement caught many by surprise, coming as it did at a time when images of the sickly chief justice, William Rehnquist, seemed to confirm the view that his would be the high court’s first resignation in 11 years. Democrats were preparing for a fight over Mr. Rehnquist’s seat, but with far less urgency than they are now in the wake of Justice O’Connor’s decision to retire, since she has often been a swing vote that has determined the outcome of cases.

Potential replacements for Justice O’Connor range from a number of U.S. Circuit Court judges to the attorney general, Alberto Gonzales. Mr. Bush is not expected to announce a nominee until after he returns this Friday from a week-long trip to Europe. The president is under pressure to choose a nominee who would support his views on social issues like abortion and gay marriage, states rights, and a strong executive role in wartime.

With senators already forming battle lines for the coming nomination process, the bipartisan agreement that cleared the way for the confirmation of several of Mr. Bush’s contentious judicial nominees may soon be obsolete. Mr. Schumer’s comments yesterday reflect strong disagreement with Republican signatories such as Mr. Graham over the conditions of the agreement.

“To simply look at the resume and say, ‘You’re fine’ – I don’t buy it,” Mr. Schumer said. “I think that person’s views on environmental rights, on voting rights, on civil rights, on women’s rights – this is the most important appointment that a president can make.”