WASHINGTON - The Democratic-led U.S. Senate must vote to confirm President Barack Obama's nominee to the U.S. Supreme Court, federal appeals court Judge Sonia Sotomayor.

With Democrats controlling 59 seats in the 100-member Senate, Republicans are unlikely to muster the 40 votes necessary to block Sotomayor's nomination with procedural tactics.

The confirmation process still could become heated as interest groups on both sides gear up for a political battle and senators probe Sotomayor's views on key issues such as abortion and torture.

Here are some questions and answers about the process:

HOW LONG WILL IT TAKE?

Since 1981 it has taken, on average, 2-1/2 months for a nominee to go to a vote by the full Senate, according to figures compiled by the Senate Judiciary Committee.

ARE MANY NOMINATIONS REJECTED?

According to the Senate historian's office, 28 of 158 nominations have been rejected, withdrawn or simply not acted upon since the court was founded in 1789. Most recently, President George W. Bush's 2005 nominee, Harriet Miers, withdrew in the face of opposition from fellow conservatives. The Senate has used the procedural roadblock known as a filibuster once: in 1968, to stop President Lyndon Johnson from making Justice Abe Fortas, a close confidant, chief justice.

COULD REPUBLICANS BLOCK OBAMA'S NOMINEE?

Barring a surprise scandal, that is highly unlikely. Republicans are certain to grill Sotomayor about topics such as abortion, torture and civil rights. But with just 40 Republicans in the now 99-member Senate (there is one opening), they would all have to stick together to deny Democrats the 60 votes needed to end a filibuster.

DURING HIS FOUR YEARS IN THE SENATE, HOW DID OBAMA VOTE ON

PRESIDENT GEORGE W. BUSH'S TWO NOMINEES?

Obama opposed both -- Chief Justice John Roberts and Justice Samuel Alito.

WHAT ARE SOME OF THE INITIAL STEPS IN THE CONFIRMATION

PROCESS?

The Judiciary Committee will send Sotomayor a questionnaire. Questions will range from date of birth, net worth and employment record to a listing of all organizations that the nominee belongs to, and a request of copies of the nominee's published writings, testimony and speeches.

WHAT HAPPENS AT THE HEARING?

Sotomayor will be invited to give an opening statement and then will be questioned by the 19-member panel, which includes 12 of Obama's fellow Democrats and seven Republicans. The hearing likely will last at least several days.

WHAT DOES THE COMMITTEE DO AT THE END OF THE HEARING?

Senators will have a week to submit written follow-up questions. Once the answers are provided, the committee will vote whether to recommend to the full Senate that she be confirmed or rejected. It could decide to send the nomination to the full Senate without a recommendation.

WHEN WILL THE SENATE VOTE?

Once the Senate receives the nomination, it will likely vote after at least a few days of debate.

WHO WILL BE KEY PLAYERS IN THE SENATE DEBATE?

Senate Judiciary Committee Chairman Patrick Leahy will head the confirmation hearing. Jeff Sessions, a conservative from Alabama, is the panel's senior Republican and will lead his party's questioning. Arlen Specter is a former Republican chairman of the committee but after his switch to the Democratic Party last month, he will be watched closely to see whether, and how enthusiastically, he backs the nominee. Democratic Leader Harry Reid and Republican Leader Mitch McConnell will play key roles in shaping the approach of their party members.

IF CONFIRMED, WHEN WILL SOTOMAYOR BECOME A JUSTICE?

Once confirmed, Sotomayor likely will head directly to the White House to be sworn. Chief Justice John Roberts probably likely administer the oath of office but if he is unavailable, another justice would handle it.

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