WASHINGTON — By choosing John Roberts to succeed William Rehnquist, President Bush offers the nation someone who already has been extensively screened, could win quick Senate confirmation and can assume the duties of chief justice with few bumps. But a difficult political calculus remains for Bush's second choice, the person who would succeed Justice Sandra Day O'Connor.

Bush originally chose Roberts, 50, a conservative appeals-court judge, to succeed the retiring O'Connor. Because Rehnquist had been battling thyroid cancer since October, the chance of a second retirement announcement continued to be a possibility.

But Rehnquist's death Saturday night arises at time of unprecedented difficulty for the Bush administration. The president has been roundly criticized for failing to act quickly to help victims of Hurricane Katrina who were stranded amid squalor and violence, without food, water, electricity or fuel. Even before the tragedy on the Gulf Coast, Bush's standing in polls was low, in part because of questions about the Iraq war.

So now the questions are whether Bush, beset with politically charged problems, will opt for a more-moderate candidate for the new opening rather than a hard-line conservative, and whether he will feel compelled to name a woman or a racial minority for the spot.

The president's decision will have long-term consequences for the nation's highest court. Rehnquist served 33 years, the last 19 as chief justice. O'Connor was in her 24th year on the bench. Roberts and whoever else is tapped could significantly affect U.S. law for decades to come.

Stakes are high

Even in the next term the stakes are high, as the justices will be taking up disputes over abortion rights, physician-assisted suicide and campus bans on military recruiting.

"I think the president has a pretty clear vision of how important the court is in the long term," says David Leitch, a former deputy White House counsel to Bush, now general counsel at Ford Motor Co.

"They'll probably do everything possible to make the best long-term decision, rather than just pay attention to the vicissitudes of the moment," says Leitch, who also was a law clerk to Rehnquist. "Thirty years from now, you might still have the [new] justice making decisions."

Marci Hamilton, a professor at Yeshiva University's Cardozo Law School in New York and a former clerk to O'Connor, says she believes there will be more pressure on the administration to go for a moderate candidate to fill what is now the O'Connor vacancy.

"The poll numbers are bad. [Hurricane] Katrina is added to other failures. The moderate choices look better politically," Hamilton says.

Leitch and Hamilton agree that Bush would seriously consider a woman or racial minority for the next justice. That could enhance the prospects for Attorney General Alberto Gonzales, a longtime friend of Bush's.

But Gonzales, 50, has a more-moderate record than Bush's conservative base has sought. Gonzales has spoken in favor of affirmative action and as a Texas judge endorsed abortion rights.

Another potential short-list candidate for O'Connor's spot is Larry Thompson, 59, who was deputy attorney general and the highest-ranking African-American law-enforcement official serving in Bush's first term. He is now senior vice president and general counsel at PepsiCo.

Other possible candidates include several federal appeals-court judges: Samuel Alito of Newark, N.J.; Janice Rogers Brown of Washington; Edith Brown Clement of New Orleans; Emilio Garza of San Antonio; Edith Jones of Houston; Michael Luttig of Alexandria, Va.; Michael McConnell of Salt Lake City; and Harvie Wilkinson of Charlottesville, Va.

Conservatives concerned

With Bush's approval ratings at an all-time low, some conservatives are worried Bush will forgo the chance to pick another conservative in favor of someone who will not provoke a fight.

Manuel Miranda, former legal counsel to Senate Majority Leader Bill Frist, R-Tenn., and founder of a conservative group that follows judicial issues, said Bush must keep his campaign promise to nominate a justice in the tradition of conservative Justices Antonin Scalia or Clarence Thomas, or risk "sinking even lower in the polls."

Congressional Democrats are feeling more emboldened by the president's weakened political standing, according to interviews with senior aides and Democratic strategists. Ron Klain, a former aide to President Clinton, said Democrats might be more willing to fight a staunchly conservative second pick.

"As his poll numbers fall, his domestic problems accumulate, and as independent voters increasingly wonder if he is out of touch with what's going on in the country, then Democrats in conservative states have less to fear by crossing him," Klain said.

The question for Democrats is whether the American public, consumed with images of the devastation in the Gulf Coast states, will tune in to the nomination hearings.