By Bill Mears, CNN Supreme Court Producer
Washington (CNN) -- The White House has begun quiet preparations for the possibility of a Supreme Court vacancy in coming months, government sources tell CNN.
Top officials have no specific information that a particular justice will retire after the court's session ends in late June, but they want to be ready for a variety of contingencies, those sources said. They requested anonymity because they are not authorized to speak on behalf of the administration.
Most of the speculation surrounds Justice John Paul Stevens, who will turn 90 in April and is the oldest of the nine-member bench. CNN previously reported Stevens has so far hired only one law clerk for the October 2010 term. Sitting justices may hire a full complement of four; retired justices are allowed one.
Sources close to him said the Chicago, Illinois, native has given no clear indication of his plans. One longtime colleague said Stevens has neither "encouraged nor discouraged any talk about his possible retirement and has actually been amused at all the attention" his future has generated in news reports and blogs.
Another source who recently spoke privately with Stevens said the justice wondered what all the fuss was about over his law clerk hiring, and said that, given his age, it didn't make sense to plan too far into the future. That source said Stevens told him he wasn't going to be rushed into making retirement decisions.
Those sources asked not to be identified because they are not authorized to speak for Stevens, who himself has refused public comment.
A high court vacancy this year would give President Obama another chance to leave his legacy on the federal judiciary. He nominated Justice Sonia Sotomayor, 56, last year, putting the first Hispanic on the high court.
Cynthia Hogan, Vice President Joe Biden's chief counsel, headed the day-to-day vetting and confirmation process for Sotomayor, and government sources said she likely would play the lead role again if a Supreme Court vacancy occurred.
Hogan also sat just behind Sotomayor during the justice's July confirmation hearings before the Senate.
Obama's new White House counsel, Bob Bauer, also is likely to have a key liaison role in handling any upcoming vacancy, given his long political experience working as an adviser to Democratic lawmakers.
Sotomayor replaced David Souter, who announced last May he would step aside after nearly two decades on the court. Those sources said that several days earlier he had discreetly given the White House notice of his plans, giving Obama's staff plenty of time to screen a list of top-level candidates.
Four women made a list of finalists whom Obama personally interviewed, among them Sotomayor, government sources said.
The other three remain in the mix for any upcoming vacancy, those sources said. The sources said they are:
• Solicitor General Elena Kagan, 49, who has no judicial experience but has impressed the White House with her skill arguing a range of important cases before the Supreme Court as the government's top appellate attorney.
• Judge Diane Wood, 59, of the Chicago-based 7th U.S. Circuit Court of Appeals. Many administration insiders believe she would be a strong intellectual force on the high court, where the newly emboldened conservative justices have achieved recent victories on campaign finance and gun rights, the sources said.
• Homeland Security Secretary Janet Napolitano, 52, a target of criticism in December over the administration's public response to the attempted bombing on a Detroit, Michigan-bound airliner.
One source said if Stevens were to retire, there would be less political pressure on Obama to name another woman to the court. Souter's exit led to universal agreement inside the White House that a woman should join Justice Ruth Bader Ginsburg, then the lone female on the court, the sources said.
Among male candidates would be a Washington-based federal appeals court judge, Merrick Garland, 58; and Cass Sunstein, 55, an old law school associate of Obama's and head of a key White House agency, government sources said.
Massachusetts Gov. Deval Patrick, 53, a longtime friend of the president's, is another name favored by some insiders, the sources said, but he has announced he will seek re-election this fall. California Supreme Court Justice Carlos Moreno, who was given serious thought for the Souter vacancy, would no longer be considered a leading candidate, observers said.
Advocacy groups expect a high court vacancy this year and already have sounded the alarm on the political and social stakes.
"If in fact Justice Stevens is stepping down, he's been a major strategist and tactician on the he court," said Nan Aron, president of the left-leaning Alliance for Justice. "The president should start putting together a list of names of individuals who can begin to change the conversation on the court and assert a leadership role."
Aron cited Wood, an appellate judge, as someone with a long record of taking strong stands on a variety of key issues.
Liberal activists have generally applauded Sotomayor's history-making elevation to the high court, her inspiring story and reliable progressive votes so far on the bench. But many said despite her qualifications, she and other liberals on the court lack the rousing rhetorical and philosophical firepower that conservatives find so appealing in Chief Justice John Roberts and Justice Antonin Scalia.
And allies on the right seem confident that in an election year filled with legislative challenges, Obama could have a much harder time choosing a high court nominee with a clear liberal portfolio.
"The burden of proof is clearly on the White House with any future Supreme Court nominations," said Gary Marx, executive director of the Virginia-based Judicial Crisis Network. "It was assumed on the last go-around that it would be more of a rubber stamp" with Sotomayor winning easy confirmation.
"But we're in an entirely new world politically. Obama, I think, wants to take a more aggressive posture and continue to appeal to his liberal base with the next court nominee, but the Democratic Senate may decide it's not in their best interest to hitch their wagon to the president."
One legal source who was deeply involved in the vetting process for Sotomayor cautioned against Obama picking what was termed a "liberal Scalia," saying "it could derail the president's entire agenda, by picking a fight over ideology. Very much in line with his philosophy of picking qualified, thoughtful judges, the president was extremely successful naming Judge Sotomayor last year. I'd expect him to follow that same path if we get something this year."
One sign of encouragement for Democrats was the president's strong tone dressing down high court conservatives in his recent State of the Union address. Obama criticized the majority's ruling giving corporations greater power to spend their money in federal elections. Justice Samuel Alito, sitting in the audience, shook his head at Obama's remarks, apparently mouthing the words "not true."
Ginsburg's name also has been floated as a possible retirement this year or next. She underwent pancreatic cancer surgery last year and has had some minor medical incidents since then.
But Ginsburg, who turns 77 next month, has reported her health is fine, and she's spending this week traveling with two court colleagues in Luxembourg for a judicial conference.
She has told friends she has no intention of leaving the job anytime soon, government sources said.