The death of Chief Justice William H. Rehnquist just days before Senate confirmation hearings for John G. Roberts Jr. set off a scramble in Washington yesterday and presented President Bush a historic opportunity to put his stamp on the Supreme Court for decades to come.

As he contemplates filling his second court vacancy, Bush is considering a plan to install Roberts as chief justice rather than as an associate justice replacing Sandra Day O'Connor, senior administration officials said. With the Roberts vetting process well advanced and his confirmation on track, such a shift could guarantee that a chief justice would be in place when the court opens its term Oct. 3.

The switch would be unprecedented in modern times. If the president does not opt for that course, officials said, he will return to the list of potential candidates he scrutinized in picking Roberts in July. Among those at the top of such a list would be his close friend Attorney General Alberto R. Gonzales; his former deputy attorney general, Larry D. Thompson; and a handful of federal appeals judges, including Edith Hollan Jones, Edith Brown Clement, J. Harvie Wilkinson III, J. Michael Luttig, Emilio M. Garza and Priscilla R. Owen.

The opening for chief justice confronted the White House with another challenge at a volatile moment. Given his deteriorating health, Rehnquist's death came as no surprise, but the timing made the politics complex, coming in the midst of a crisis touched off by Hurricane Katrina and just before the Roberts hearings, which are set to begin tomorrow.

While senators discussed postponing the hearings, Bush advisers gathered at the White House to consider strategy amid recovery efforts in the Gulf Coast. Some conservative advocacy groups laid down markers, urging Bush not to appoint Gonzales, whom they consider too moderate.

As they sift through names, White House advisers are weighing whether it would be better to announce a nominee quickly or to wait until after the situation in the Gulf Coast is better in hand and the Roberts confirmation process is finished. With his poll ratings at an all-time low, gasoline prices at a longtime high and U.S. troops suffering rising casualties in Iraq, Bush confronts a perilous point in his presidency.

Bush mentioned none of this in his public comments yesterday, instead paying tribute to Rehnquist in a brief televised appearance in the Roosevelt Room and promising to move expeditiously in naming a chief justice.

"There are now two vacancies on the Supreme Court, and it will serve the best interests of the nation to fill those vacancies promptly," Bush said. "I will choose in a timely manner a highly qualified nominee to succeed Chief Justice Rehnquist."

Bush praised Rehnquist for a "powerful intellect," a "deep commitment to the rule of law" and a "profound devotion to duty." In a personal note, the president recalled Rehnquist's special effort to appear at the inauguration in January despite his thyroid cancer to swear Bush in for a second term. "I was honored, and I was deeply touched when he came to the Capitol for the swearing-in last January," Bush said. "He was a man of character and dedication."

The president later telephoned Rehnquist's children to express condolences and ordered flags flown at half-staff. Rehnquist will lie in repose in the Great Hall of the Supreme Court building starting tomorrow and will be buried at Arlington National Cemetery on Wednesday. If his successor has not been confirmed by the time the court reconvenes next month, his chair will remain empty and draped in black.

For Bush, the situation represents a rare chance to cement a more conservative court and his own legacy at the same time. No sitting justice has died while in office in more than a half-century, and no president has installed two newcomers to the court at the same time since 1971, when Richard M. Nixon appointed Rehnquist to fill one of a pair of vacancies. When President Ronald Reagan tapped Rehnquist to move up from associate justice to chief justice in 1986, it created an opening that was filled by Antonin Scalia. If Bush elevates Scalia or Clarence Thomas to chief justice, it would mean three confirmation battles at once.

"This is the most historic moment in Supreme Court history in our lifetime, no question about it," said Jay Sekulow, chief counsel at the American Center for Law and Justice, founded by evangelist Pat Robertson, and an adviser to the White House on court issues. "These are justices who are going to serve for decades."

The chief justice casts only one vote on the nine-member court but wields influence in important ways. As the titular leader, the chief justice can try to set a tone and philosophical direction. When in the majority on a case, the chief chooses which justice writes the decision, shaping the contours and scope of a ruling. The chief also runs the court's administrative functions as well as those of the broader federal judiciary.

With Rehnquist's death, the senior associate justice fills in as chief -- in this case Justice John Paul Stevens, the court's most consistent liberal voice. For that reason alone, Republican advisers said, the White House will be eager to get a replacement for Rehnquist in place. Also, an eight-member court can divide on 4 to 4 votes that would let lower court decisions stand without setting precedent.

Bush began meeting yesterday with senior aides, including Chief of Staff Andrew H. Card Jr. and White House counsel Harriet Miers, to discuss possible nominees. Aides pulled out files from candidates considered in July.

"We're not starting from standing still," said one senior official, who like others declined to be named because Bush insists on a confidential process. "We have a process that has been developed . . . and now we're in an execution phase." The official said the decision and its timing would be independent of the hurricane relief efforts. "I don't think Katrina will influence that," he said.

Bush seems unlikely to name Scalia because he wants someone young enough to be chief for a generation, advisers said, nor is he likely to ask O'Connor to become chief, as some Democratic senators urged on television yesterday. Although Clement, a judge on the U.S. Court of Appeals for the 5th Circuit, was a finalist behind Roberts, several Republicans close to the White House said they doubted she would be named chief justice.

The idea of making Roberts chief justice seems to have natural appeal. Roberts, a former lawyer in the Ronald Reagan and George H.W. Bush administrations who now serves as a judge on the U.S. Court of Appeals for the District of Columbia Circuit, was first interviewed by the White House in April not for O'Connor's seat but in the expectation that Rehnquist would retire or die.

As a former Rehnquist clerk, Roberts could be expected to continue in the same conservative course, and at age 50 he would have a long tenure in the top slot. After six weeks of media scrutiny, he is also a known commodity who has not generated strong opposition among Senate Democrats.

The mechanics of a switch would not be hard. Bush would withdraw Roberts's nomination as associate justice and then simultaneously nominate him as chief justice. Bush could then take his time choosing someone else to replace O'Connor because she has agreed to remain on the court until her successor's confirmation. The president would also be free to focus more intently in the days and weeks ahead on leading the federal response to Katrina.

"That's the right move for a whole variety of reasons and, if I were on the inside, that is what I would be arguing," said Bradford A. Berenson, a former associate White House counsel in the president's first term. "There is one and only way for the Supreme Court to start its term with nine members and a chief, and that is to nominate John Roberts."

Administration officials said the option was under consideration but would not handicap how likely it is. "Roberts is obviously qualified to be chief justice," one top official said. "The question is if there are arguments on the other side, and there are. We just have to weigh them."

One of the arguments on the other side is not to do anything to complicate a confirmation process for Roberts that has gone smoothly. And Bush knew when he picked Roberts for associate justice that he probably would have a chance to name a chief justice, so he might already have someone else in mind.

If so, some Republican strategists believe it could be Gonzales, a longtime confidant from Texas who served as White House counsel in Bush's first term and would be the first Hispanic to serve on the Supreme Court. Many conservatives howled last summer at the prospect of Gonzales replacing O'Connor because they view him as unreliable on abortion, affirmative action and other key issues, and they renewed the complaints within hours of Rehnquist's death.

"I don't know what they get by alienating the last remaining 35 percent of the country that's really on his side," said a conservative ally of the White House who would comment only if granted anonymity.

But Bush likes Gonzales and might feel compelled to keep the court from becoming too much of a white man's bastion, advisers said. "The pressure to find a woman or a minority if anything will be even greater this time around," Berenson said. Another close adviser to the White House who asked not to be named said, "I have a sneaking suspicion it would be either a woman or Gonzales."