White House officials have said they expect the president to pick his nominee by early May.

Stevens, who turned 90 on Tuesday, is a leading liberal on the court.

Obama says he wants to replace him with an intellectual candidate with consensus-building skills who could be persuasive on a court with a 5-4 conservative majority.

The president has already begun talking to some of the candidates he is interested in and this week reached out to potential candidates for the pending Supreme Court vacancy.

He is considering breaking with tradition if he follows the advice of some fellow Democrats who have  urged him to look beyond judges in his pick of a candidate for the Supreme Court.

Obama is considering a list of about 10 candidates, including politicians, judges and a former Harvard Law School dean.

He has said he hopes to find a candidate who will understand the struggles of ordinary Americans.

Some Democrats have called for Obama to select someone who did not attend Ivy League law schools, or for a liberal voice to rival conservative justice Antonin Scalia.

Senate Judiciary Chairman Patrick Leahy and former President Bill Clinton are among Democrats who see benefits in selecting someone with political or policy experience.

But it remains unclear which names on the White House short list are being given the most serious scrutiny.

In recent decades, US presidents have tended to turn to judges to fill vacancies on the Supreme Court, although historically plenty of politicians have been tapped for the court.

The idea to tap a non-judge is not new.  President George W. Bush nominated his longtime aide Harriet Miers, who was shunned by conservatives so aggressively that she eventually withdrew from the process.

One of the more prominent defenders of the current high court is the nominee who sailed through the nomination process right before Miers’ failure: Chief Justice John Roberts.

A new national poll released this week suggests that a majority of Americans expect Obama to appoint a liberal to the Supreme Court, but only one in four want that to happen.

Whomever the president selects must be approved by the Senate, and the Supreme Court’s role in decisions on hot-button social issues such as abortion and gun ownership rights has made the nomination process a political battleground in recent decades.

Analysts have said the fight over Obama’s court pick may be more intense in a congressional election year than it was last year when Obama tapped Sonia Sotomayor to become the court’s first Hispanic justice.