The Senate Democratic leader, pressed by several allies to build as much opposition as possible to Supreme Court nominee John G. Roberts Jr., said yesterday he will vote against President Bush's choice for chief justice. But Sen. Harry M. Reid of Nevada conceded that Roberts will be confirmed easily next week and "will get plenty of votes" from his fellow Democrats.

Reid's announcement, made in a closed party caucus luncheon and then a Senate speech, came as Democratic senators are struggling with the first chief justice confirmation in 19 years. Many party activists want them to show as much solidarity against Roberts as they can muster. Not only does Roberts's conservative philosophy deserve it, they argue, but it also would serve as a warning to Bush that Democrats will fight vigorously if Bush names someone even further to the right to succeed centrist Justice Sandra Day O'Connor this fall.

An opposing strategy, which Senate insiders described as less persuasive, argues that the party should show a willingness to accept Roberts while saving energy for an all-out battle in case Bush's next nominee is notably more conservative. Reid, Majority Leader Bill Frist (R-Tenn.) and two other senators will meet with the president today to begin discussing how to replace O'Connor.

Reid said he decided to oppose Roberts because the nominee withheld too much information from senators and because government memos he wrote in the 1980s raised troubling questions about his views, especially on civil rights.

"I was prepared to look past these memos, and chalk them up to the folly of youth," Reid said in his speech. But in last week's Judiciary Committee hearing, he said, Roberts adopted "what I consider a disingenuous strategy of suggesting that the views expressed in those memos were not his views. . . . We should only vote to confirm this nominee if we are absolutely positive that he is the right person" for a lifetime appointment on the nation's highest court.

Reid, an antiabortion lawmaker from a state that Bush carried in 2000 and 2004, said he made clear to colleagues that he was speaking as an individual, not as a minority leader trying to steer his caucus. "This is something people have to vote their conscience on," he told reporters.

Roberts's confirmation is a foregone conclusion in the Senate, where Republicans hold 55 of the 100 seats. The only question is how many Democrats will support him, and what political signal it will send. Party liberals hope no more than 15 Democrats, mostly from states Bush carried, will vote yes. That would result in a 70 to 30 confirmation vote. But Sen. Kent Conrad (D-N.D.) recently told reporters: "I think he can get from 75 to 80 votes."

Members of both parties said partisanship and interest-group politics have sharpened over the past decade to the point that a unanimous Supreme Court confirmation vote -- such as the one Justice Antonin Scalia received in 1986 -- is a thing of the past.

The Senate Judiciary Committee will vote tomorrow on recommending Roberts's confirmation, and most of the eight Democratic members appeared torn after meeting privately yesterday morning. The only member who has clearly signaled that he plans to oppose Roberts is Edward M. Kennedy (D-Mass.).

The committee's ranking Democrat, Patrick J. Leahy (Vt.), said Sunday he had drafted a "for" speech and an "against" speech. Aides yesterday said it was unclear which he will deliver today on the Senate floor.

Some Democratic activists said the party risks alienating its contributors by not uniting against Roberts. "Many, many people in the donor base are feeling discouraged and want to see the Democrats fight back," said Ellen Malcolm, president of Emily's List. "If they see Democrats falling in line with Republicans, they're going to say, 'There's no need for me to support them.' "

Malcolm said prospective 2008 presidential candidates face the wrath of party activists if they support Roberts, and then he and the majority of the court rule against abortion rights.

Perhaps no Democrat is being watched more closely than Sen. Hillary Rodham Clinton (N.Y.), who has been trying to emphasize her centrist credentials. When asked for her thoughts on Roberts yesterday, she playfully mimed with nods, shrugs and an enigmatic smile.

Both of her husband's high court nominees -- Ruth Bader Ginsburg and Stephen G. Breyer -- won strong Republican support. But on Sunday, former president Bill Clinton drew a clear distinction between those battles and the fight over Roberts's nomination, suggesting reasons Democrats might oppose Roberts that may provide cover to his wife.

The former president said there were no partisan disputes over the withholding of documents in the case of his nominees, as there have been with Roberts. He also noted that, with two vacancies to fill, Bush has the ability to shift the balance on the court and that without knowing who his second choice is, Democrats may be more cautious about backing Roberts.

"The only question is whether the Senate has an extra burden here because it's likely to have a significant impact on the balance of court decisions, depending on who the next nominee is," Clinton said on ABC's "This Week" on Sunday. "I think if President Bush nominated a clear moderate before the vote happened in the Roberts case, he would sail through."

With no suspense but the final vote count left in the Roberts contest, senators from both parties are focused on Bush's next nomination. Reid said Democrats will consider it "a sharp poke in the eye" if Bush taps any of the 10 appellate court nominees who were blocked -- permanently or temporarily -- by Democratic-led filibusters in Bush's first term. That would include Judges Priscilla R. Owen and Janice Rogers Brown, who have been mentioned as possible nominees.

Would he try another filibuster? a reporter asked. "I'm just saying I would be terribly upset," Reid replied.

"We should only vote to confirm this nominee if we are absolutely positive that he is the right person," Senate Minority Leader Harry M. Reid (Nev.) said in a speech on the Senate floor.