After winning a bruising battle for a fifth term, Sen. Arlen Specter (R-Pa.) is struggling to keep the fruits of victory with the same aggressiveness, agility and finely honed survival skills that have marked most of his idiosyncratic 24-year career on Capitol Hill.

He is in line to achieve his long-sought goal of chairing the Senate Judiciary Committee but could be denied the post by fellow Republicans as a result of a furious backlash among conservatives about his post-election comments suggesting the Senate is likely to reject staunchly antiabortion nominees to the Supreme Court.

Many major conservative groups -- including the Family Research Council, Traditional Values Coalition and Concerned Women for America -- have called for Specter's rejection, with some of them bitterly recalling that Specter joined with Democrats in blocking the Supreme Court nomination of Robert H. Bork, a conservative hero, in 1987.

"The problem with Senator Specter is not merely his warning to President Bush on judicial nominees," said Family Research Council President Tony Perkins, "but a political career full of positions more suitable for the likes of John Kerry or Ted Kennedy than a Republican senator from Pennsylvania."

The campaign against Specter represents an effort by conservatives to lay down their markers in the coming battles over Bush's anticipated Supreme Court nominations. The stakes are high because the chairman wields considerable power within a committee that may consider as many as four nominations to the court during Bush's second term. Christian antiabortion groups are planning a "pray-in" on Capitol Hill tomorrow to try to block Specter.

With phone calls, television appearances and sit-down chats, Specter is working hard to convince skeptical colleagues that he will push for swift action on Bush's judicial nominations, regardless of whether they share his views in favor of abortion rights.

Publicly at least, Specter shrugs off his latest challenge, contending that conservative groups are gunning for him now after failing to defeat him in a GOP primary earlier this year. "It's an occupational hazard . . . just another bump in the road," he said in an interview last week.

Specter could be blocked by a majority vote of either committee Republicans or the full Senate GOP caucus. The showdown is officially scheduled for early January but could come as soon as this week when Congress returns for a post-election session. Specter appears to have made some headway, but the White House has been tepid in its support of the maverick Republican, and the Senate GOP leadership has not weighed in on his behalf. Specter's fate remains in doubt.

Appearing yesterday on "Fox News Sunday," Majority Leader Bill Frist (R-Tenn.) called Specter's comments "disheartening" and said the Pennsylvanian had "not yet" made a persuasive case for the chairmanship. Frist said Specter will meet this week with the Senate GOP leadership as well as Judiciary Committee Republicans but that a final decision will not be made until January.

Frist also said he is determined to stop Democrats from filibustering judicial nominations and again suggested one option would be a majority vote of the Senate to declare such filibusters unconstitutional, an idea that has prompted angry protests from Democrats.

Sen. John McCain (R-Ariz.) said on ABC's "This Week" that he supports Specter and thinks he would become chairman.

Specter, also appearing on ABC, defended his record, reiterating that he never has and never would impose a litmus test on judicial nominees. Asked whether he would support Supreme Court Justice Clarence Thomas if Bush nominated him as chief justice, Specter declined to answer, saying votes should not be taken through "sound bites on national television."

At 74, Specter is the dean of a vanishing breed in Congress, a Republican moderate and abortion rights advocate in a party dominated by antiabortion conservatives. He frequently finds himself in a pivotal position on close votes, enhancing his power but often irritating colleagues of both parties as he weighs his choices. Just as he enraged conservatives by opposing Bork, he infuriated liberals with his prosecutorial treatment of Anita F. Hill on sexual harassment charges that Hill brought against Thomas during his 1991 confirmation hearings.

A loner with a contrarian streak and a sometimes abrasive manner, Specter is more respected than liked, admired by colleagues for his hard work, keen legal mind and prosecutorial skills developed as a district attorney in Philadelphia. He is an outsider's insider, using his incumbency and committee positions to spread federal dollars through Pennsylvania, earning the gratitude of many voters who do not share his political views. "A lot of people who don't like him say, 'Yeah, he was there when we needed him,' " said G. Terry Madonna, a political scientist at Franklin & Marshall College in Lancaster, Pa.

He enjoys the perks of power, including foreign junkets tailored to meet his unusual demands, such as air-conditioned squash courts and suitable partners. But colleagues also say he is an especially diligent lawmaker who demands as much of himself as his staff.

Specter is also a nimble political operator who has straddled the liberal-moderate-conservative ideological line on taxes and other major issues, giving him ammunition to fend off attacks from both left and right, as he did in his most recent reelection campaign. He is a thoughtful and courageous pragmatist, according to friends, and a wily opportunist, according to critics.

"He's a very smart man and a very hardworking politician who always wants to have it both ways," said Rep. Joseph M. Hoeffel III (D-Pa.), his opponent in the Nov. 2 election. Democrat Lynn Yeakel, who almost defeated Specter 12 years ago, put it more harshly, calling him "a back-and-forth windshield-wiper kind of senator."

"He considers the issues, one by one," responded David Urban, a former Specter chief of staff. "That's not being an opportunist; that's being thoughtful." Sen. Patrick J. Leahy (Vt.), ranking Democrat on the judiciary panel, agreed: "He's an independent thinker, which is what a senator is supposed to be."

Throughout his career, Specter has sometimes toed the GOP line and sometimes crashed through it. Congressional Quarterly ranked him 48th of 51 GOP senators in support for Bush's positions in 2003. Often he makes mid-course corrections, as he did in voting against legislation to ban what critics call "partial birth" abortions and then voting to override President Bill Clinton's veto of the bill. Sometimes he offers complicated, legalistic explanations that confound both enemies and friends.

This is one of those moments.

With his reelection, Specter was poised under the Senate's seniority tradition to succeed Judiciary Committee Chairman Orrin G. Hatch (R-Utah), who must relinquish the post under the Senate GOP's six-year term limits for chairmen. But at a post-election news conference, Specter said, in words that lent themselves to varying interpretations, that it is unlikely the Senate would confirm a Supreme Court nominee who would overturn the 1973 Roe v. Wade decision establishing a woman's right to an abortion.

"When you talk about judges who would change the right of a woman to choose, overturn Roe versus Wade, I think that is unlikely," Specter said at the Nov. 3 news conference. He noted that he previously said the Roe decision is "inviolate" and did not back away from that characterization.

Even though Specter expressed similar sentiments during the campaign, conservative groups immediately mobilized to oppose him, flooding Senate offices with demands that Republicans reject him as judiciary chairman. Relying on some news accounts of his remarks, they interpreted the comments as warning the White House against sending antiabortion nominees to the Senate and suggesting he would apply a "litmus test" to block nominees who oppose abortion rights.

Specter promptly denied he had issued a warning to the president, saying he was "very respectful of his constitutional authority on the appointment of federal judges." Nor, he said, has he suggested any kind of litmus test. He noted that he has voted for all of Bush's first-term judicial nominations and supported the confirmation of William H. Rehnquist as chief justice even though Rehnquist opposed the Roe decision. "I expect to support the president's nominees," he said in interviews.

He was simply stating the political facts of life, Specter said: that Republicans next year will be five votes short of the 60 needed to break a Democratic filibuster that is almost certain if Bush names a resolutely antiabortion person to the Supreme Court.

But Specter's entanglement with Supreme Court nominees -- from Bork to the current controversy -- has had deep and enduring consequences.

Although he says no one has raised any substantive fault with his combative interrogation of Hill, it helped inspire the 1992 "Year of the Woman" in politics and nearly cost Specter his Senate seat to Yeakel.

And it did nothing to mollify conservatives, who continue to evoke the memory of Bork after 17 years. "He ran for reelection in 1986 as someone who would help get President Reagan's nominees approved . . . and then turned around and dealt a lethal blow to Bork," complained Douglas Johnson, legislative director for the National Right to Life Committee. "He's a chameleon."

But Johnson and others also suggested a broader concern over Specter.

"Many Republicans fear an opportunity to govern would be squandered by someone who doesn't share the core principles of the party," said Rep. Pat Toomey (Pa.), a conservative who gave Specter a scare in the Pennsylvania GOP primary last spring.

Some Republicans are especially miffed that Specter appeared to distance himself from Bush during the campaign, even after Bush weighed in on behalf of Specter during the primary, apparently figuring Specter would be the stronger defender of the seat in November.

In the Senate, Specter has championed tough anti-crime laws, more spending for education and health research and, more recently, more federal support for embryonic stem cell research.

Specter's independent streak showed through vividly when he tried to invoke Scottish law to vote "not proven" during Clinton's impeachment trial. Rehnquist, who was presiding over the trial, was not impressed and recorded Specter as voting for acquittal.

Sen. Arlen Specter (R-Pa.) caused a backlash among conservatives after he suggested that it is unlikely the Senate would confirm a Supreme Court nominee who would overturn the 1973 Roe v. Wade decision.