Factbox: Possible replacements for Justice Stevens

(Reuters) - U.S. President Barack Obama is expected to announce his nomination to replace retiring Supreme Court Justice John Paul Stevens within the next few weeks, with the news generally seen coming in early May.

The White House has not identified any candidates to replace Stevens, considered the court's leading liberal. But following is a look at some potential contenders, according to Obama administration officials and legal experts.

* Elena Kagan, 49, is U.S. solicitor general, appointed in January 2009 to argue cases before the Supreme Court. She is the first female solicitor general, working at the U.S. Justice Department as the federal government's top appellate attorney.

A former Harvard Law School dean, Kagan was a finalist for last year's Supreme Court vacancy before Obama selected U.S. appeals court Judge Sonia Sotomayor of New York.

Kagan, known for her keen legal intellect, won support from conservatives at Harvard. She served as associate White House counsel to President Bill Clinton in the 1990s and taught at the University of Chicago Law School, where Obama also taught.

She was a clerk to Supreme Court Justice Thurgood Marshall, whose appointment in 1967 marked the last time a solicitor general had been appointed to the Supreme Court.

Kagan was confirmed as solicitor general by a 61-31 Senate vote. Some Republicans voiced concern about her lack of courtroom experience and opposition to on-campus military recruiting at Harvard because of U.S. policy barring homosexuals from serving openly in the armed forces.

* Diane Wood, 59, a U.S. appeals court judge in Chicago, knows Obama from teaching at the University of Chicago Law School. She also had been among the finalists for last year's Supreme Court opening.

Wood served in the U.S. Justice Department's Antitrust Division during the Clinton administration and is considered a top expert on international competition law.

She is a strong supporter of abortion rights and is seen as a moderate liberal who could provide an intellectual counterpoint to the court's conservative majority.

Nominated to the appeals court by Clinton in 1995, Wood won unanimous confirmation by the Senate.

* Merrick Garland, 57, is a U.S. appeals court judge in Washington, D.C. Born in Chicago, he is considered a moderate known for writing thorough, well-reasoned opinions.

Clinton named Garland to the appeals court and in 1997 he won Senate approval by a 76-23 vote. He had worked in the U.S. Justice Department during the Clinton administration as a top aide to the deputy attorney general.

Garland's responsibilities included supervising the investigation into the 1995 Oklahoma City bombing and the prosecution of "Unabomber" Theodore Kaczynski, who killed three people and injured 23 in a bombing campaign.

* Sidney Thomas, 56, is a liberal judge on the Ninth Circuit Court of Appeals in San Francisco, considered the most liberal in the United States.

A former lawyer in Montana and graduate of the University of Montana law school, Thomas was appointed to the Ninth Circuit by Clinton.

He would be an outsider candidate without close ties to the White House. His 15-year liberal judicial record also would provide ample hints at how he might handle high court decisions.

* Jennifer Granholm, 51, is in her second and final term as Michigan's first female governor. Michigan's economic crisis, massive job losses and an ailing auto industry have been blamed for her low approval ratings. Term limits mandate that she must leave office this year.

The Canadian-born Granholm, a Democrat and Harvard Law graduate, was previously the state's attorney general, focusing on consumer protection and individual rights. She has served as an assistant U.S. attorney and county corporation counsel, but has never been a judge.

A member of Obama's transition team, she was considered for last year's Supreme Court vacancy, but was not a finalist.

* Janet Napolitano, 52, Obama's homeland security secretary and a former Democratic governor of Arizona, also was a finalist for the vacancy that went to Sotomayor.

She was recently subjected to scathing criticism over her response to a failed Christmas Day airplane bombing attempt.

In 1991, she was an attorney who helped represent law professor Anita Hill, who charged Clarence Thomas with sexual harassment during Senate committee hearings on his nomination to the Supreme Court. That case helped spur Senate Republicans to hold up her nomination for more than a year when Clinton nominated her as U.S. attorney for Arizona in 1993.

* Cass Sunstein, 55, is Obama's regulatory czar, overseeing governmental regulation, and a former teacher at Harvard and the University of Chicago law schools.

Obama is known to think highly of Sunstein, especially in the fields of constitutional and administrative law.

Sunstein has advocated a judicial minimalism philosophy that judges should try to narrowly decide each specific case and avoid sweeping changes in the law.

(Compiled by James Vicini and Patricia Zengerle; Editing by Eric Beech)