WASHINGTON — The death of William Rehnquist leaves President Bush with his second Supreme Court opening in four months and sets up what's expected to be an even more bruising confirmation battle than that of John Roberts.

The president could elevate to chief justice one of the court's conservatives, such as Antonin Scalia or Clarence Thomas, but it's more likely he will choose someone from outside the court.

Possible replacements include Attorney General Alberto R. Gonzales and federal courts of appeals judges J. Michael Luttig, Edith Clement, Samuel A. Alito Jr., Michael McConnell, Emilio Garza, and James Harvie Wilkinson III. Others mentioned are former Solicitor General Theodore Olson, lawyer Miguel Estrada and former deputy attorney general Larry Thompson.

Already preoccupied with the recovery effort for Hurricane Katrina and the Roberts nomination battle, Bush now must also focus on picking a successor for Rehnquist. But Rehnquist's battle with thyroid cancer has prepared the White House for the possibility that he would be leaving the court, so the element of surprise should be less than it was in the case of Sandra Day O'Connor's retirement.

It was not immediately clear what impact Rehnquist's death would have on confirmation hearings for Roberts, scheduled to begin Tuesday.

The process of selecting and confirming a new justice will probably last past the first day of the court's new term, Oct. 3. That means that even if Roberts is swiftly confirmed, the court will operate with only eight members for an indefinite period.

Tie votes on the court result in the automatic affirmance of the lower court's ruling in the court, but do not establish a legal precedent.

"The president and Mrs. Bush are deeply saddened at the passing of Chief Justice Rehnquist," the White House said in a statement. "His family is in their thoughts and prayers."

An aide said Bush was informed of Rehnquist's death shortly before 11 p.m. and added that the president will make a statement to reporters about the chief justice this morning after attending church services.

Interest groups — anticipating that Rehnquist's announcement last fall that he has thyroid cancer would lead to his retirement — have spent months raising millions of dollars and researching potential candidates. One group has stockpiled $18 million to help confirm whomever Bush picks. An opposition group has set up a "war room" from which to launch its attacks on the eventual nominee.

Some of that money and passion have already been spent supporting and fighting the Roberts nomination.

The last time there were simultaneous vacancies at the court was 1971, when Justices Hugo Black and John Marshall Harlan retired in September, about a week apart. Rehnquist, then a Justice Department lawyer, urged the Nixon administration to move fast in replacing them and wound up being appointed to Harlan's seat himself.