The Senate may have averted its "nuclear" confrontation over judicial filibusters. But just as the end of the Cuban missile crisis did not settle the Cold War, it was clear Tuesday that the compromise by a bipartisan group of 14 senators has not solved the battle over judicial nominations.

Even as the Senate voted overwhelmingly Tuesday to end the blocking tactic known as the filibuster for the nomination of Priscilla Owen, and prepared to do the same for California Supreme Court Justice Janice Rogers Brown and a third nominee, William Pryor, Democrats and Republicans said the true test of the compromise could come as early as this summer.

That's when many observers expect Supreme Court Chief Justice William Rehnquist to step down because of thyroid cancer. President Bush would then nominate a replacement to a narrowly divided court that serves as the final arbiter of many contentious issues in a narrowly divided country. And the amorphous provision at the heart of the agreement would take center stage.

It could undo the whole deal.

The seven Democrats who signed the compromise agreed to stop blocking Owen, Brown and Pryor in exchange for a vow from seven Republicans not to support a GOP plan to outlaw the filibuster for judicial nominees. The compromise also states that future nominations could only be blocked by the filibuster "under extraordinary circumstances."

Any other circumstances would lead to a breech of the agreement, which could give Republicans the votes they need to again trigger their controversial plan, known as the `nuclear option" for the havoc it could cause in the normally collegial Senate.

But the definition of "extraordinary circumstances" is left to the "discretion and judgment" of each senator signing it, according to the two-page text. Tuesday, some Republicans and Democrats differed on exactly what that phrase meant.

Sen. Lindsey Graham, R-S.C., who signed the agreement, said, "the fact that you're conservative is no longer an extraordinary circumstance." But another signer, Sen. Ben Nelson, R-Neb., said that political ideology could be an extraordinary circumstance for a nominee "so far out of the mainstream."

It led some senators to wonder whether the compromise simply kicked the problem of judicial nominees down the road - the same road that a future Supreme Court nominee would have to travel.

"Keep in mind this is merely a truce," said Sen. Orrin Hatch, R-Utah. "It's not a treaty yet, because an awful lot depends on good faith on the part of the seven Democrats on the other side and the seven Republicans on our side - and every other Republican and Democrat in the Senate."

Backers of the compromise said Tuesday that they expected it to hold because it was brokered in good faith among a group that has promised to keep the lines of communication open...

With the compromise depriving the party of enough votes to continue the filibuster of Owen, whom Democrats had blocked since Bush nominated her in May 2001, a measure to stop it passed overwhelmingly Tuesday, 81-18. Feinstein and 25 other Democrats joined with all 55 Republicans to end the filibuster. The last time there was such a vote on Owen's nomination to the Fifth Circuit Court of Appeals in New Orleans, only two Democrats voted to end the filibuster; it takes 60 votes to succeed.

Feinstein said she will still vote against Owen's confirmation - a final vote is expected Wednesday - but saw no reason to continue backing the filibuster. Sen. Barbara Boxer, D-Calif., however, was one of the 18 who voted to continue the blocking tactic. She said she will do the same on Brown and Pryor when they come up for votes, probably after the Memorial Day recess.

"I just wanted to send the message that I'm going to continue to work to defeat her," Boxer said of Owen, a justice on the Texas Supreme Court. "She's way out of the mainstream, and this is an extraordinary circumstance for me."

And there's the potential problem with that phrase. Boxer and Senate Minority Leader Harry Reid, D-Nev., say Democrats already had been reserving the filibuster for extraordinary circumstances, noting that the party had blocked just 10 of Bush's 218 judicial nominees.

But Sen. John Cornyn, R-Texas, said Democrats have used the filibuster too frequently and without cause for well-qualified nominees such as Owen and Brown.

"Looking at the litany of false charges makes me skeptical that any nominee no matter how qualified, no matter how deserving ... some of our colleagues will find the circumstances extraordinary," Cornyn said. "So it's clear to me that this agreement among these 14 - of which 86 senators were not a party - does not solve anything. What it does do is perhaps delay the inevitable."