WASHINGTON — In nearly 25 years on the Senate Judiciary Committee, Sen. Arlen Specter has sat through nine Supreme Court confirmation hearings, some short and polite, some ugly and drawn out. Now that he's the chairman, he is prepared for the next one to go either way.

"I'm not going to anticipate a bruising battle," Specter said Friday after Justice Sandra Day O'Connor announced her resignation, "but I'm not going to run from one either."

Specter, R-Pa., is already engaged in one bruising battle, against Hodgkin's disease, for which he is undergoing chemotherapy. Although he may not anticipate another battle, just about everyone else in Washington, D.C., is, and the inevitable confirmation fight could be the defining moment in his long career.

Perhaps more than any other senator, Specter will be the pivotal figure as he tries to manage his bitterly divided committee, his own uneasy relationship with the White House and the intense pressure that is bearing down on him from the left and right at a time both sides are deeply suspicious of him.

Within hours of O'Connor's announcement, Specter said he would probably hold confirmation hearings in September, a move that could upset conservatives, who would like to move a nominee along as quickly as possible in the hope of outflanking liberal groups that plan to use the summer to prepare for a confirmation battle.

Sharp-tongued and cagey, with an uncanny knack for parsing his words to wiggle his way out of tight spots, Specter is widely regarded as the Senate's brightest legal mind.

A rare centrist in a Senate that has shifted increasingly to the right, he is reviled by conservatives for dooming the Supreme Court nomination of Robert Bork in 1987, and by liberals for assuring the confirmation of Justice Clarence Thomas in 1991 with his aggressive questioning of Anita Hill, the law professor who had accused Thomas of sexual harassment.

The vacancy created by the retirement of O'Connor gives Specter, 75, a chance to rewrite his Judiciary Committee history, but it comes at a delicate time for him. He nearly lost his chairmanship last year amid an uproar from conservatives, who were furious when Specter, a supporter of abortion rights, suggested the Senate would have difficulty confirming judges who would overturn Roe v. Wade.

He won the job after an all-out campaign that culminated with a carefully worded four-paragraph statement in which he pledged to "use my best efforts to stop any future filibusters," the tactic Democrats had been using to block President Bush's judicial nominees. The filibuster fight could re-emerge during a Supreme Court confirmation, and a big question is how Specter would handle it.

"I'll jump off that bridge when I come to it," he said.

Keeps own counsel

So far, Specter has not been forced to jump. Last month, when Sen. Bill Frist, the Republican majority leader, brought the Senate to the brink of a vote to bar judicial filibusters, Specter kept the chamber on tenterhooks, refusing to say how he would vote even as he urged party leaders to "liberate their caucuses to vote without party straitjackets."

When 14 senators — 7 Democrats and 7 Republicans — struck a deal to avert the so-called nuclear option, Specter was not part of it. His critics were exasperated.

"Arlen Specter is as predictable as the sun rising in the east," Richard Viguerie, the conservative direct-mail consultant, complained at the time. "He's not going to make a deal he keeps with anybody."

But Specter said he was keeping his own counsel, a move he considers wise and one that will probably continue to confound Specter-watchers as the nomination process moves forward. "I've made people mad saying very little, so I'm not going to say very much," he said.

He added: "I think a senator, whether or not he is the chairman, ought to be circumspect in what he says."

That may be especially so for the chairman of the Judiciary Committee, whose members include some of the most powerful lawmakers in the Senate, including fellow Republicans Charles Grassley of Iowa and Orrin Hatch of Utah and Democrats Patrick Leahy of Vermont, Edward Kennedy of Massachusetts, Joseph Biden of Delaware and Charles Schumer of New York.

But Specter was not circumspect Friday about criticizing Democrats who were already vowing to use the filibuster against a nominee they find objectionable.

"I'm a little bit concerned about what I heard Senator Kennedy say on television tonight: that if the president does not nominate someone who meets Senator Kennedy's specifications, as he articulates it, the American people will expect a battle and they're prepared to do it," he said.

"I would hope that we would tone down the rhetoric," he added.

Consultation urged

Democrats have been pressing Bush to seek their advice on possible nominees, and Specter said he had urged the president to consult him and three other senior senators: Frist; Harry Reid of Nevada, the Democratic leader; and Leahy, the senior Democrat on the Judiciary Committee. The president apparently took Specter's advice and has invited the four men to the White House on July 11, after the Senate returns from recess.

Specter is not one to shun the limelight — he is scheduled to appear on three morning talk shows today — and he has never masked his moderate views. Last year, he survived a bitter primary challenge from the right, winning re-election with considerable help from Bush.

In 1995, he made a brief ill-fated bid for the White House, running on the unusual platform of attacking Christian conservatives in his party.

Personal challenge

The Supreme Court hearings come at a time of great personal challenge for Specter. His chemotherapy treatments have left him tired, he said, although he pushes himself to get up in the morning and play his regular squash game.

"Frankly," he said, "it's hard to get out of bed, hard to do the exercises and hard to get going, but once I'm on the squash court, I'm fine."

He has been very public about his illness — "I decided a long time ago: no toupee, no baseball hat," he said, referring to the baldness that resulted from his treatment — and has become a symbol for cancer patients, who have been sending him cards and letters. He advises them to keep a busy schedule.

Perhaps for that reason, Specter may have been the only politician in Washington, D.C., to publicly speculate that Chief Justice William Rehnquist, who has thyroid cancer, would not retire.

"I think I have special insights into how he feels," Specter said, although he said they have not talked about it. "I think the chief likes to get up every day knowing he has important work to do, and I like to get up every day thinking I have important work to do."

A former prosecutor, Specter entered public life four decades ago as a lawyer for the Warren Commission, which conducted the inquiry into the assassination of President Kennedy. Specter was elected to the Senate in 1980 and immediately sought a seat on the Judiciary Committee, to the chagrin of the chairman, Sen. Strom Thurmond, R-S.C. The conservative Thurmond, concerned that Specter was too liberal, tried to keep him off the committee, but when no one else wanted the last remaining seat, Specter got it.

Specter has participated in the confirmation of every one of the current Supreme Court justices except John Paul Stevens, and he says he views himself as "a fact-finder" rather than a prosecutor.

He pledged to run the hearings "straight down the center, professionally," and added that he was eager to delve into a detailed examination of the nominee.

He has said repeatedly that he has no regrets about either the Bork or the Thomas confirmations.

He says he is not looking at the upcoming hearings as any measure of his legacy: "It's too early to think about my legacy."