WASHINGTON -- At the conclusion of this week's hearings for Supreme Court nominee John G. Roberts Jr., many of the same conservative leaders who vigorously fought Senate Judiciary Committee Chairman Arlen Specter's ascent to that post last year were showering him with compliments for his handling of the hearings.

It was a moment of vindication for Specter, who plans to give a Senate floor speech Monday announcing how he will vote on Roberts' nomination. But the Pennsylvania Republican senator was already focusing on how much more combative his arena could become when President Bush selects a successor for the court's swing vote, retiring Associate Justice Sandra Day O'Connor.

Late yesterday, Bush invited Specter as well as the Judiciary panel's ranking Democrat, Vermont Sen. Patrick Leahy, along with Senate Majority Leader Bill Frist, R-Tenn., and Senate Minority Leader Harry Reid, D-Nev., to a White House breakfast meeting Wednesday morning to consult, presumably on that next nominee -- signaling that the controversial decision may not be far off.

Alluding to the difficulties that could lie ahead, Specter noted in an interview this week the Democrats' "pent-up frustration" after they failed to elicit Roberts' views on issues such as abortion and end-of-life decisions, and how it was likely to spill over into the next hearings.

"Bush disarmed the left by choosing Roberts," Specter said. "They couldn't get out of the starting gate."

The elements for a more explosive next confirmation battle were falling into place at week's end. O'Connor's power as a swing vote magnifies the next nominee's ability to shift the court in a way that a replacement for the late Chief William H. Rehnquist would not.

As the Roberts hearings wrapped up, moderate Senate Democrats distanced themselves from the suggestion that their party would block him with the parliamentary delaying tactic known as a filibuster -- which requires 60 votes to break in a Senate divided among 55 Republicans, 44 Democrats and one independent -- allowing the minority party to keep that weapon in their arsenal for the next nominee.

Roberts -- with his keen intelligence, substantive resume and imperturbable demeanor -- has already set the bar extraordinarily high for the next nominee, even in the view of liberals like Sen. Charles E. Schumer, D-N.Y., who told the nominee in his closing remarks that he may well "possess the most powerful intellect of any person to come before the Senate for this position."

Specter, the only committee Republican who supports abortion rights, may have set a high bar for himself as well this week.

Last November, Specter created a conservative uproar by saying he thought it was "unlikely" that judges who would "change the right of a woman to choose," by voting to overturn Roe v. Wade, could get confirmed in the narrowly divided Senate. After that fracas, it would have seemed inconceivable that conservatives would be describing Specter's performance in the terms they used this week.

Jan LaRue of Concerned Women for America, among many others, said last fall that Specter had disqualified himself for the chairmanship and that giving in that post would be like asking filmmaker Michael Moore to lead the Republican National Committee. But this week in an interview, LaRue described Specter as fair, even commending his performance in a news release.

Wendy Long, legal counsel for the conservative Judicial Confirmation Network, said Thursday that Specter had done "the perfect job as chairman, which is to maintain strict discipline in the committee, ... and with this crowd, that is no small feat.

"With his own questions," she said, "he asked them vigorously, ... but he was certainly respectful of the nominee."

Leonard Leo, executive vice president of the conservative Federalist Society, described the Pennsylvania senator's performance as "spectacular." He said "conservatives were really nervous" about Specter last year because "they weren't sure the chairman would understand that there's a bit of difference between being a rank-and-file member of the committee, where you can be a maverick, and being chairman, where you really do have to be an umpire."

But when Specter posed the first set of questions on the right to privacy and the way that relates to Roe v. Wade, Leo said, he helped mollify Democrats and "set a tone" for the rest of the hearings. "I would much prefer to have Chairman Specter asking [Roberts] those questions than a hysterical Democrat," Leo said. "It always helps to have someone who is viewed a little more objectively running the proceedings."

Even officials at Focus on the Family, a group that stridently opposes abortion, whose leaders last fall blasted Specter as "untrustworthy" and revved up opposition to his chairmanship, said they did not believe that the chairman had crossed an antagonistic line with his questions this week.

Bruce Hausknecht, a Focus on the Family judicial analyst, said Specter could have been more of a champion of Roberts. Still, he went on to say, "Specter tested [Roberts] once or twice but then let the witness answer the way he wanted. I think we can grade him at above-average."

But LaRue said she found a lot to "fault with Senator Specter's questioning," particularly his query about whether Roberts thought Roe v. Wade was "super-duper [legal] precedent."

"You can only go so far," LaRue said. "Trying to get [Roberts] to commit to upholding Roe, ... it was inappropriate."