Washington - President Barack Obama faces a classic political dilemma in picking a new Supreme Court justice.

He must decide whether to nominate an individual liberal enough to carry on John Paul Stevens' legacy on issues such as abortion rights and the death penalty or move toward a more moderate candidate in hopes of winning enough Republican support to avoid a debilitating Senate confirmation battle.

His decision is likely to dominate the political landscape this summer, just months before midterm elections that will determine who controls Congress.

A bitter fight threatens Democratic hopes of focusing on the economy and job creation. It also would be a major distraction to Obama as he tries to push ahead on other parts of his agenda, including education and energy legislation.

If the president chooses an outright liberal nominee, it might help rally his Democratic base - crucial for the party in midterm elections - but would surely provoke a knockdown fight with Republicans. At the same time, if he picked someone less objectionable to Republicans, it could further alienate dispirited liberal Democrats who complain that Obama sold out on elements of health care overhaul. And it might not even work in attracting GOP votes.

As the anti-government tea party movement revs up, rank-and-file Republicans are sounding more energized, more eager to court the party's base - and possibly more likely to portray anyone Obama picks for the Supreme Court as too liberal.

"The Republicans are going to do everything possible just to drag this out," said American University political scientist James Thurber. "It's going to be ugly."

Stevens, the strongest liberal voice on a conservative-leaning court, said Friday he will step down when the court finishes its work in late June or early July. His long-anticipated announcement came 11 days before his 90th birthday.

Obama praised Stevens as an "impartial guardian" of the law, and said he would move quickly to name a nominee. "It is in the best interests of the Supreme Court to have a successor appointed and confirmed before the next term begins," Obama told reporters in the Rose Garden.

But the mood in Washington soured noticeably and the dynamics in the Senate have changed since Obama named Sonia Sotomayor to the high court last year.

Democrats then had the 60 votes needed to stop a Republican filibuster. Even so, Sotomayor won some GOP votes and a serious filibuster was never attempted.

That majority is a luxury Obama no longer has. Democrats are now able to deliver only 59 votes at most, with some senators worrying about their re-election prospects.

Obama couldn't find a single Republican vote in the Senate for his health care overhaul and Republicans have marched in lock step against nearly all of his other top domestic priorities.

Republicans aren't ruling out an attempt to block the president's nominee, even though they risk overplaying their hand by filibustering a Supreme Court nomination - or trying to postpone the vote until after the November elections in hopes of holding more GOP votes.

Even before Stevens' announcement, Republicans were taking a hard line on Obama's judicial nominees. Top GOP senators on Friday were quick to signal a rocky time ahead by asserting that Obama's new nominee would be subjected to the closest of scrutiny.

"There's going to be a whale of a fight if he appoints an activist to the court. That's not good for him, it's not good for the Senate, it's not good for the country," said Sen. Orrin Hatch, R-Utah, a member of the Judiciary Committee.

"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," said Senate Republican Leader Mitch McConnell of Kentucky.

Among the potential nominees mentioned are three who were considered last year for the vacancy filled by Sotomayor - Appeals Court Judges Diane Wood and Merrick Garland and Solicitor General Elena Kagan.

Norman Ornstein, a politics scholar at the American Enterprise Institute, said all three were "clearly well-qualified and not outside the bounds of normal judicial philosophy."

Ornstein said if Obama names someone to the court like those jurists and not "some radical or somebody with enormous ethical problems," he doubts Republicans could successfully block confirmation. "It'll still be a fight," he said. "It could have come at a better time. But I think it's one he can handle."

Whomever Obama selects, fireworks seem certain before the volatile Senate Judiciary Committee.

"It's the most contentious committee in the United States Senate. Its members - Republicans and Democrats - are the Senate's most formidable ideological warriors," said Ross Baker, a political science professor at Rutgers University who took a sabbatical from teaching several years ago to work for Sen. Patrick Leahy, D-Vt., the committee's current chairman.

Baker said it will be extremely hard for Obama to find a nominee suitable to Republicans, particularly on the Judiciary panel, as "ideological interest groups on both sides go into high mobilization."