The Senate Judiciary Committee will demand that Supreme Court nominee Samuel A. Alito Jr. answer more questions than did Chief Justice John G. Roberts Jr., and it may subject him to extra hours of grilling to do so, the panel's chairman said yesterday.

But Sen. Arlen Specter (R-Pa.), said he senses little enthusiasm among Democrats for a filibuster to block Alito, and he believes the nominee's fate will turn largely on "how credible he is" at the panel's confirmation hearing, which begins Jan. 9.

"His nomination faces some real hurdles," Specter said in an hour-long interview with Washington Post editors and reporters. Senators will not allow Alito to sidestep as many questions as Roberts did during his confirmation hearing, he said, because Alito has far more judicial opinions to defend and because he wrote two controversial memos on abortion and other matters in 1985.

One of the memos asserted that the Constitution "does not protect a right to an abortion." The other, which Specter described as "a very strident advocacy memo," outlined Alito's advice on how "to advance the goals of bringing about the eventual overruling of Roe v. Wade," the landmark 1973 decision that legalized abortion in all 50 states. Both memos were written when Alito, now 55, was a lawyer in the Reagan administration's Justice Department.

Specter, who supports abortion rights, said he will start the hearing by pressing Alito on his abortion views. "There are a lot of big, big issues that he has to answer, but this is the one which has captured the public's imagination," the chairman said.

"Judge Alito will have to answer more questions than Judge Roberts did," Specter said.

Roberts managed to deflect several questions about his views on abortion and other topics -- sometimes to Specter's irritation -- but still won Senate confirmation comfortably on Sept. 29 after lawmakers in both parties hailed his mastery of constitutional issues. Republican and Democratic senators will be tougher on Alito, Specter said, in part because his two 1985 memos seem to state a vigorous and enthusiastic opposition to abortion rights and some forms of affirmative action programs.

Specter said he will ask Alito, "What assurances can you give to this committee -- and the American people and all the litigants that will come before your court -- that your personal views will not have any impact, any weight, on your judicial decisions?" The senator said, "His reception is going to depend upon how credible he is."

Specter noted that Alito has been an appellate judge for 15 years and therefore has ruled in far more cases than Roberts did in his two years on the appeals court. "If you go to his 300-plus cases, you can paint him in a lot of different shades of a lot of different colors," Specter said of Alito.

He said "there's a good chance" that Alito will spend more time before the committee than did Roberts, who faced 21/2 days of questions. But he said his plan is to conduct the entire hearing -- including senators' opening statements and outside witnesses -- in one week, allowing the full Senate to vote on whether to confirm Alito by the end of January.

Democrats have not ruled out a filibuster against Alito, but Senate Minority Leader Harry M. Reid's aides generally avoid mentioning the word. A filibuster would prevent a confirmation vote unless the nominee's supporters mustered 60 votes to end debate. Republicans hold 55 of the chamber's 100 seats. But chances of a filibuster appear "remote at this stage," Specter said, because "there is nothing they can point to" that suggests Alito is outside the judicial mainstream.

Specter has met twice in private with Alito. He later told reporters that the nominee said his personal views on issues such as abortion will not determine how he would rule from the bench. Asked about his reaction to Alito's comments, Specter said yesterday: "I don't have a comfort level, I have an open mind."

Meanwhile yesterday, three liberal groups said they will announce their opposition to Alito's confirmation today. They are the Congressional Black Caucus, the House Democratic Women and the Washington-based National Women's Law Center.

Senate Judiciary Committee Chairman Arlen Specter said he does not think Democrats will try to filibuster the court nomination.