A pair of key Senate Republicans urged President Obama on Sunday to pick someone from the judicial mainstream to succeed retiring Supreme Court Justice John Paul Stevens, and downplayed -- but did not rule out -- a filibuster to block a nominee they opposed.

Sen. Jeff Sessions (R-Ala.), the ranking Republican on the Judiciary Committee, said a filibuster would be in the offing only if Obama picked “a nominee that evidences a philosophy of ‘judges know best,’ that they can amend the Constitution by saying it has evolved . . . then we’re going to have a big fight about that because the American people don’t want that.”

Jon Kyl of Arizona, the Senate’s second-ranking Republican, said a filibuster could be “easily avoided” if Obama appointed someone with a conventional legal outlook.

Democratic Sen. Charles E. Schumer of New York, who appeared with Kyl on ABC’s “This Week,” responded, “It’s just about a certainty that the president will nominate someone in the mainstream, so the likelihood of filibuster is tiny.”

Stevens, 89, announced his retirement Friday and will leave the court when its term ends in June or July.

Judiciary Committee Chairman Patrick J. Leahy (D-Vt.), appearing on NBC’s “Meet the Press,” said “there’s no question” a new justice will be confirmed before the start of the court’s fall term, when it begins hearing new cases.

Four possible nominees were discussed Sunday: Solicitor General Elena Kagan; Homeland Security Secretary Janet Napolitano; Judge Diane Wood, who sits on the Chicago-based U.S. 7th Circuit Court of Appeals; and Judge Merrick Garland of the U.S. Court of Appeals for the District of Columbia Circuit, which, after the Supreme Court, is considered the nation’s most influential bench.

Kyl and Sessions declined to assess the acceptability of any of the four, though Kyl pronounced all of them at least nominally qualified.

The two Republicans’ comments are likely to have little influence on Obama as he ponders his selection, said Trevor Parry-Giles, a communications professor at the University of Maryland and author of a book on the Supreme Court confirmation process.

“I don’t think they’re going to give him an easy time of it, no matter who he picks,” Parry-Giles said.

Choosing a Supreme Court justice “has become a ritualized process” in which early statements by opposition leaders like Kyl and Sessions are meant to galvanize their political base rather than advise the president, Parry-Giles said.

“What they stated was sort of the obvious,” he said. “You could have written the script before they said it.”

Filibustering a Supreme Court nominee has emerged as a possibility since Democrats lost their 60-seat supermajority with the January election of Sen. Scott Brown (R-Mass.), but many observers consider it unlikely.

Stevens’ departure would not alter the Supreme Court’s conservative tilt, although he has exerted unusual influence within the nine-member panel. That complicates the political calculations that go into making a selection, said Douglas Kendall of the liberal-leaning Constitutional Accountability Center.

Stevens is the leader of the court’s liberal wing, a skilled opinion writer who is adept at forging alliances with other justices, including Anthony M. Kennedy, who frequently is the court’s swing vote.

Obama “should concentrate on finding someone who can fill at least some of those roles, not whether he can pick or avoid a fight,” Kendall said.

azajac@tribune.com