A week after Justice Sandra Day O'Connor announced her retirement, the White House and its allies are preparing for the possibility that Chief Justice William H. Rehnquist might soon follow suit, opening up a second vacancy to fill and scrambling the politics of this summer's brewing nomination battle.

Talk of a possible Rehnquist retirement has reached full boil again as Republican strategists mapped out plans for how to tackle a double nomination. Advisers inside and outside the White House are discussing how to select two potential nominees, how they might match or balance each other and how to sequence their confirmation hearings.

"We're prepared for every contingency," said a senior administration official, who spoke on the condition of anonymity because Rehnquist has made no announcement. "If it's multiple candidates, we'll be ready."

If Rehnquist decides to step down, President Bush will have the opportunity to put a decisive personal stamp on a closely divided Supreme Court that has seen no turnover for the past 11 years. Such a scenario would almost certainly escalate the high-decibel, high-dollar political showdown both sides already expect.

Twin vacancies would present Bush with an intriguing choice: Does he use the opportunity to appoint two reliable conservatives who would shift the court away from what he sees as improper judicial activism on divisive issues such as abortion, religion in public life and gay rights? Or does he try to balance competing impulses by filling one seat with a conservative who would strictly interpret the Constitution and the other with his friend, Attorney General Alberto R. Gonzales, who is less favored by the right but would be the first Hispanic on the nation's highest court?

"If we get a second vacancy, then there's just a lot up for grabs," said Gary L. Bauer, a prominent Christian conservative leader who ran for president in 2000. "It would mean a tremendous battle."

For the moment, Rehnquist's intentions remain unclear. The chief justice has not informed the White House of his plans, according to administration officials, and predictions that he would retire at the end of the court's term last week proved unfounded, or at least premature.

Yet in the days since O'Connor surprised the capital with her announcement, speculation in Washington has grown that Rehnquist was merely waiting to let her go first. At age 80, Rehnquist is fighting thyroid cancer, and he missed months of oral arguments during the last term. Quoting unidentified court sources, columnist Robert D. Novak wrote yesterday that Rehnquist would retire by the end of the week. Others around the capital said they were calibrating strategies in the event he does.

Several officials and Republican strategists cautioned against presuming any quick retirement, figuring that Rehnquist would rather stay as long as physically possible and that he may resent feeling railroaded by public speculation about his future. But even if Rehnquist makes no immediate announcement, the White House and its political allies assume that the seat ultimately will open, meaning Bush can plan for two nominations eventually.

"I'm prepared if it happens tomorrow morning or two years from now," said Jay Sekulow, chief counsel of the American Center for Law and Justice, who has been advising the White House on court strategy. "You have to operate under the assumption right now that it's likely to happen."

Only twice in recent times has a president nominated two justices for the Supreme Court in tandem. In 1971, Richard M. Nixon filled the seats of John Marshall Harlan and Hugo Black with Rehnquist and Lewis F. Powell Jr. In 1986, Ronald Reagan elevated Rehnquist from associate justice to chief justice, succeeding Warren E. Burger, and named Antonin Scalia to fill Rehnquist's seat. Some Republican strategists point out that Bush could elevate Scalia to chief justice, leaving him with three opportunities to put his personal imprint on the court -- but also three confirmation battles to wage simultaneously.

"It would put a lot of pressure on the system if he retired now," said former White House counsel C. Boyden Gray, another key outside strategist aiding the White House. "God, it would make it an interesting summer. It's going to be interesting enough as it is."

Even factoring Scalia out of the equation, Bush has different calculations for a chief justice than for O'Connor's seat. In looking for a chief justice, some White House advisers said, they would consider management experience and look for a deeper legal resume than for an associate justice.

If Rehnquist does retire, the advisers said, then the White House must decide whether to fill his seat first and let a replacement for O'Connor go second as she indicated in her retirement letter that she would continue to serve until a successor is confirmed. And Bush must decide whether to package a staunch conservative with a less conservative nominee such as Gonzales in hopes of satisfying various constituencies enough to ease confirmation, or to favor a bolder approach by advancing two reliable conservatives.

If Rehnquist does not retire right away, Bush faces a similar choice, in that he could go with a conservative first and wait to nominate Gonzales for the next opening, or the other way around. But in picking an O'Connor replacement now, he would have to hold back the nominee he actually wants for chief justice.

"I may be totally wrong on this, but I think he means to change the court and that he would not be sending a balancer-type candidate," said Paul M. Weyrich, chairman of the Free Congress Foundation and a leading conservative voice in Washington. "Now it could be that friendship with Gonzales outweighs that. I don't know. But in the discussions I've had with him, he seems generally committed to changing the composition of the court."

"We would say, 'Look, pick two awesome constructionists,' " or jurists who strictly interpret the Constitution, said Sean Rushton, executive director of the Committee for Justice, a group formed to support Bush nominees. "The country would like to shift the court to a more solid majority of constructionists or whatever you want to call it. I think the public is fed up with the courts handing down rulings like the pledge and the Ten Commandments and the property case," three recent cases that have sparked controversy.

Conservatives have warned against Gonzales because they see him as too moderate on abortion and affirmative action. Bush has bristled at the attacks and called on his supporters to tone down their rhetoric.

In his first comments on his prospects, Gonzales said in an interview published yesterday that he was not campaigning to become a justice but his comments did not rule it out either. "I've been asked since 2001 whether or not I'd consider going on the court, and I've consistently said, 'I'm not a candidate for the Supreme Court' -- and that remains true today," Gonzales told the Denver Post during a visit to Colorado. "I love being attorney general. My job, currently, is to help the president make this decision."

The White House presumes that Democrats will fight anyone it nominates and found reinforcement for this view in comments by Sen. Charles E. Schumer (D-N.Y.) overheard on his mobile telephone while riding a train to New York. "We are contemplating how we are going to go to war over this," Schumer was reported saying on the Drudge Report Web site.

Schumer's office did not dispute the account. "If they put forward an extremist nominee, we will not just simply roll over," said his spokesman, Israel Klein. "But he has stated over and over again, he hopes for a consensus nominee who will get broad support in the Senate."

Republican strategists said there is no such person for Bush to find and therefore he should not fall into the trap of trying. "I don't think he's looking for consensus nominees," said Sekulow, noting that Bush has often praised Scalia and Clarence Thomas as his models for a Supreme Court justice. "I think the president meant what he said and said what he meant."

Chief Justice William H. Rehnquist has led the court since 1986.