Stevens said in newspaper interviews on the Web Saturday that he will decide soon on the timing of his retirement, whether it will be this year or next. Stevens, the leader of the court's liberals, turns 90 this month and is the oldest justice.
His departure would give Mr. Obama his second nomination to the court, enabling him to ensure there would continue to be at least four liberal-leaning justices. The high court is often split 5 to 4 on major cases, with the vote of moderate Justice Anthony Kennedy often deciding which side prevails.
"I will surely do it while he's still president," Stevens told The Washington Post.
But Stevens, who was named to the court by President Ford, a Republican, in 1975, says he still loves the job, and says he continues to write the first draft of his own opinions.
Stevens says if it ever gets to point where he stopped doing that, it would be a sign he wasn't up to the job anymore.
Stevens is the second-oldest justice in the court's history, after Oliver Wendell Holmes. He is the seventh-longest-serving justice, with more than 34 years on the court.
Another liberal, Justice Ruth Bader Ginsburg, had surgery last year for early-stage pancreatic cancer. While Ginsburg has been her usual energetic self, including frequent speaking engagements and a teaching stint in Europe, long-term survival rates for pancreatic cancer are low.
Ginsburg, 77, has said she intends to serve into her early 80s, and she has hired her clerks for the court term that begins in October 2010.
Justices are reluctant to retire in bunches, mainly because they want the nine-member court as close to full strength as possible.
Stevens also is nearing two longevity records. When he joined the court, he replaced the longest-serving justice, William O. Douglas, and would need to serve until mid-July 2012 to top that service record. He would surpass Holmes as the oldest sitting justice if he were to remain on the court until Feb. 24, 2011.
"I do have to fish or cut bait, just for my own personal peace of mind and also in fairness to the process," Stevens told The New York Times. "The president and the Senate need plenty of time to fill a vacancy."