WASHINGTON (Reuters) - Liberal Supreme Court Justice John Paul Stevens announced on Friday he would resign, and President Barack Obama promised to name a successor quickly, setting the stage for an expected partisan election-year Senate confirmation battle.

Stevens, one of the oldest and longest-serving justices in history, sent a letter notifying Obama of his retirement this summer. Stevens, who turns 90 in 11 days, joined the court in 1975 after being appointed by President Gerald Ford.

An administration official said Obama was considering about 10 potential nominees to replace Stevens.

At the White House, Obama paid tribute to Stevens and said his nominee, like Stevens, would know that powerful interests must not be allowed to drown out the voices of ordinary citizens.

“I will seek someone in the coming weeks with similar qualities -- an independent mind, a record of excellence and integrity, a fierce dedication to the rule of law, and a keen understanding of how the law affects the daily lives of the American people,” Obama said.

A bruising confirmation battle could sidetrack Democratic plans to focus on the economy and job creation ahead of November’s congressional elections in which Republicans hope to regain control of Congress.

In the Senate, which will vote on the nomination, Democrats praised Stevens and urged Obama to name someone who can continue his legacy while Republicans promised thorough scrutiny of any nominee.

Obama is expected to choose someone who will follow the same basic judicial philosophy as Stevens and is unlikely to change the court’s overall ideological balance, which has been closely divided with five conservatives and four liberals.

Stevens has supported abortion and gay rights and gun restrictions and opposed the death penalty. In recent major business cases, he wrote rulings allowing lawsuits against tobacco and pharmaceutical companies.

Obama said he would move swiftly to name a nominee to ensure the new justice was seated for the court’s new term in October. Stevens is retiring at the end of the current term, which lasts through June.

Senate Republican Leader Mitch McConnell made clear his party would be heard in the confirmation process.

“Americans can expect Senate Republicans to make a sustained and vigorous case for judicial restraint and the fundamental importance of an even-handed reading of the law,” he said.

TWO-EDGED SWORD

The opportunity to make a second appointment to the high court in just two years is a double-edged sword for Obama.

It gives him a chance to put his stamp on the court but also is likely to stall his agenda in Congress amid partisan bickering. Obama has made a series of centrist decisions that have angered both Republicans and liberal base.

Last year, he named Sonia Sotomayor as the court’s first Hispanic, replacing Justice David Souter. She was confirmed on a largely party-line vote of 68-31.

Among the leading candidates for the opening are Solicitor General Elena Kagan and U.S. appeals court judges Diane Wood and Merrick Garland.

Supreme Court Justice John Paul Stevens poses for an official photograph at the Supreme Court, September 29, 2009. REUTERS/Jim Young

Wood is one of the nation’s top experts on international competition law while Garland and Kagan do not have much of a record in business cases.

All are considered moderate liberals and could face varying degrees of Republican opposition. But even conservative activists said each probably would win a simple majority vote in the Senate, where Democrats hold 59 of 100 seats.

The confirmation battle could dominate Congress for some time and make it tougher for Obama’s fellow Democrats to focus on reducing the U.S. unemployment rate, expected to be a key issue in congressional elections.

It also could complicate last-ditch efforts by some Democrats and Republicans to win Senate passage of compromise legislation to combat global climate change.

POLITICAL BATTLE

U.S. Senate Judiciary Committee Chairman Patrick Leahy, who will chair the confirmation hearing for Obama’s nominee, said he expected the president to consult members of both political parties before making his pick.

“I hope that senators on both sides of the aisle will make this process a thoughtful and civil discourse,” Leahy said.

There was no immediate indication on when the confirmation hearings would be held but it likely will be before Congress departs for its August recess in advance of the November congressional elections.

Supreme Court appointments have become major political battles in Congress. The high court decides contentious social issues such as abortion and the death penalty and high-stakes business disputes.

It is too early to say what major issues the court will confront in the future. Among the handful of cases to be decided next term, the justices will consider whether vaccine manufacturers can be sued for damages and a free-speech case about anti-gay protests at funerals for U.S. military members killed in Iraq.