|Sandra Day O'Connor|
The last Supreme Court vacancy came 11 years ago during the Clinton administration, so the Bush White House and opposition Democrats have had plenty of time to plan for a Senate confirmation battle.
Supreme Court appointments are often an important part of a president's political legacy, and President Bush is expected to make his choice known sometime after he returns from a European trip on July 8.
"I have directed my staff, in cooperation with the Department of Justice, to compile information and recommend for my review, potential nominees who meet a high standard of legal ability, judgment and integrity, and who will faithfully interpret the Constitution and the laws of our country," Mr. Bush said.
Opposition Democrats are urging the president to appoint a moderate to the high court, and avoid what could become a highly partisan and drawn out confirmation battle in the Senate.
"If the president abuses his power, and nominates someone who threatens to rollback the rights and freedoms of the American people, then the American people will insist that we oppose that nominee, and we intend to do so," Democratic Senator Ted Kennedy from Massachusetts said.
Justice O'Connor was appointed to the bench by President Ronald Reagan, a Republican, in 1981.
But she often pleased liberals by her opinions and votes on issues such as abortion rights and the death penalty.
Senate Republicans say they are ready to proceed with the confirmation process, once the president formally nominates his choice to replace Justice O'Connor.
Pennsylvania Republican Arlen Specter chairs the Senate Judiciary Committee, the panel that will hold the confirmation hearings.
"She [O'Connor] has occupied a pivotal role on the court as a centrist. With many 5-4 ecisions, which the court has handed down, she has been the critical vote," said Senator Specter.
Political and legal analysts predict the confirmation battle will be drawn out because of Justice O'Connor's record as a judicial centrist and a key swing vote on the high court.
Justice O'Connor once told a television interviewer that she did not often agree with that label.
"I think that is something the media has devised as a means of writing about the court, and I do not think that has a lot of validity," she said.
But a Supreme Court expert at the American University in Washington, Professor Stephen Wermiel, says conservative and liberal activist groups are gearing up for a major confirmation fight that could last most of the next few months, no matter who the president nominates.
"I do not think there is anybody on any list, who will not lead to some kind of fight. The stakes are too high," he said. "There are too many constituent groups, with too much interest in where the court is headed on all different sides of the political spectrum. And, so, I do not see any way to avoid having a real battle."
Most Supreme Court experts had predicted that a retirement announcement was more likely to come from Chief Justice William Rehnquist, who is battling thyroid cancer. But Justice Rehnquist gave no indication of his plans, as he presided over the end of the high court's annual term this past week.