Supreme Court Justice John Paul Stevens, the court's oldest member, announced his retirement today, giving President Obama his second high court appointment and setting the stage for a contentious confirmation battle in the Senate this summer.

The leader of the liberal bloc of four justices, just 11 days short of his 90th birthday, recently signaled his intent to step down soon to assure that Obama would name his replacement.

The announcement came in a 67-word letter delivered to the White House at 10:30 a.m. and relayed by White House Counsel Bob Bauer to the president, who was aboard Air Force One returning from Prague.

For the president, the court vacancy presents another challenge to his hopes to be seen as focusing on jobs and the economy now that the lengthy battle over health care is finished. The White House has a list of potential justices left over from last year's nomination of Justice Sonia Sotomayor. But a nomination battle risks crowding out other issues.

Among those considered last year and still high on the White House list for this vacancy are Solicitor General Elena Kagan, federal Appeals Court Judges Diane Wood of Chicago and Merrick Garland of the District of Columbia and Homeland Security Secretary Janet Napolitano.

Kagan, Wood and Napolitano were interviewed by the president last year before he picked Sotomayor.

Any of them would likely settle into the court's liberal bloc, but none would be able to carry the influence of Stevens, whose long tenure gave him added clout. They would all but guarantee added scrutiny from Republicans in the Senate who used their statements today to warn the president not to pick a replacement they would deem as too liberal.

The Senate Judiciary Committee is likely to follow a routine and timetable similar to what was used for Sotomayor. She was nominated May 26, with committee hearings beginning 39 days later. After four days of hearings, the committee voted 13-6 for Sotomayor on July 28, and was confirmed the following week, 68-31. The process lasted 72 days.

Obama gave no hint of his timetable for naming a nominee, except to say he would "move quickly." In what seemed to be a reference to the court's recent ruling allowing corporate spending on campaigns, the president said his choice would "be someone who, like Justice Stevens, knows that in a democracy, powerful interests must not be allowed to drown out the voices of ordinary citizens."

Stevens, who joined the court in 1975, said his retirement would take effect the day after the court finishes its work for the summer, most likely in late June. This, he said, would give the Senate time to confirm a successor before another term begins in October.

Without a nominee, Senate Judiciary Chairman Patrick Leahy gave no indication of the timetable he will follow. But he implored all senators to "make this process a thoughtful and civil discourse." Senate Majority Leader Reid urged Republican senators to join in "fair, respectful hearings and swift confirmation."

Republicans were more cautious, and in no hurry.

Senate Minority Leader Mitch McConnell promised "a sustained and vigorous case for judicial restraint and the fundamental importance of an even-handed reading of the law." Sen. Orrin Hatch, R-Utah, a former chairman of the committee, warned Obama against "an activist judge, who would substitute their own views for what the law requires," saying such a nominee "is not qualified to serve on the federal bench."

Senate Judiciary ranking member Jeff Sessions promised a "fair and thorough" hearing for Obama's nominee. But, in a lengthy statement, he said he would guard against any effort by the president to put forth a nominee who shows "empathy" instead of a strict adherence to the law. "That approach," he said, "is deeply unpopular with the American people."