Each time senators asked Sandra Day O'Connor about her views on a specific topic like abortion during her Supreme Court confirmation hearings in 1981, she looked down at a piece of paper that had been prepared for her and read, "I do not believe as a nominee I could tell you how I would vote."

This response, known in the Senate as "taking the judicial Fifth," has been recited in one form or another by every recent Supreme Court nominee, and it is almost certain to be used this year by whomever President Bush chooses to replace Justice O'Connor.

It is bound to frustrate some senators and interest groups, since the new justice will be the swing vote on important issues like affirmative action, the role of religion in public life, states' rights, environmental protection and laws on partial birth abortion.

But as a practical matter, senators have no real recourse when a nominee declines to answer questions. They can hardly refuse to confirm the nominee on that ground alone, since so many other justices who have been noncommittal on the issues of the day have been approved.

In 1986, for instance, Antonin Scalia refused even to say whether he subscribed to the principle of Marbury v. Madison, the fundamental decision in 1803 that established the authority of the Supreme Court to strike down laws as unconstitutional. The Senate confirmed him unanimously....

Senator Edward M. Kennedy, Democrat of Massachusetts, who as a member of the Judiciary Committee has questioned every Supreme Court nominee since the Johnson administration, said that if President Bush picked a candidate because of his or her judicial philosophy - about as safe a bet as can be placed in today's political climate - then senators deserved to learn about that philosophy....

Mr. Kennedy took a different tack in 1967, when he was supporting Johnson's nomination of Thurgood Marshall to be an associate justice. Then, Mr. Kennedy argued that judicial philosophy was not a proper line of questioning and that senators should stick to examining the candidate's "background, experience, qualifications and temperament."

The senator who has consistently been most outspoken over the years in his belief that candidates for the Supreme Court should undergo rigorous scrutiny by the Senate is Arlen Specter, who is now chairman of the Judiciary Committee.

In his autobiography, "Passion for Truth," published in 2000, Mr. Specter, a Pennsylvania Republican, wrote that the Senate should reject nominees who refuse to "answer questions on fundamental issues" and added: "In voting whether or not to confirm a nominee, senators should not have to gamble or guess about a candidate's philosophy but should be able to judge based on the candidate's expressed views."...

Mr. Specter's views were shaped in large part by his experience questioning Robert H. Bork, an appeals court judge whom President Ronald Reagan nominated to the Supreme Court in 1987....

At the outset of his confirmation hearings, Judge Bork declared, "I cannot, of course, commit myself as to how I might vote on any particular case." But Judge Bork had written and spoken extensively and provocatively on issues like free speech, sex discrimination, "equal protection of the laws," abortion and sexual privacy, and there was no way he could escape questions on such matters. Mr. Specter was especially aggressive in his questions, and Judge Bork often recanted and qualified his controversial views in ways that satisfied no one.

The Senate rejected the nomination, 58 to 42, with Mr. Specter voting against his fellow Republican. In the aftermath, Judge Bork said that the intense questioning of him on constitutional issues was improper and that the only people who could stand such scrutiny and be confirmed were those with such thin records on constitutional topics that they could duck the questions.

That proved to be prescient three years later, when President George Bush picked David H. Souter for the court. Mr. Souter had been a Supreme Court justice in New Hampshire and had essentially no record on constitutional issues. When topics like abortion came up at his hearings, Mr. Souter took the "judicial Fifth," and he won confirmation from a Senate controlled by Democrats.

To the disbelief of some senators, Clarence Thomas, also nominated by the first President Bush, said he had never really thought about or discussed whether Roe v. Wade, the ruling establishing a constitutional right to abortion, had been decided properly.