TODAY THE SENATE Judiciary Committee begins its much-awaited hearings on the nomination of Judge John G. Roberts Jr. to serve as chief justice of the United States. Since Judge Roberts's professional qualifications -- his competence in the law, integrity and judicial temperament -- are not at issue, the hearings chiefly represent an opportunity to explore his judicial personality. Judge Roberts is a conservative, but what does that mean? The hearings should not be expected to produce a detailed road map to how a Chief Justice Roberts would decide the many controversial matters about which the court must rule. A nominee, bound by ethics, cannot be expected to telegraph how he or she is likely to vote on a pending case, so confirmation hearings tend to produce a degree of tension between the nominee's reticence and the desire on the part of senators to understand the package they are being asked to buy. But the public should expect to gain a better sense of how Judge Roberts would approach cases, and the extent to which he has a strongly ideological bent.

The first critical area that senators should probe is Judge Roberts's attitude toward what is called stare decisis, the doctrine that pre- cedents should typically be followed by the courts in the name of the stability of the legal system. Those who disagree with Judge Roberts's views would have less reason to worry about his confirmation if they were confident that he is likely to honor precedents, in contrast to Justice Clarence Thomas, who generally regards the doctrine as being of limited value in constitutional law. This is a difficult area to examine with great precision: For example, despite the great respect for pre- cedent, the "separate but equal" world that existed before Brown v. Board of Education in 1954 would be unacceptable today. Senators should press Judge Roberts to articulate the factors, in addition to original error, that he would insist upon seeing before overturning a decision of the court.

Another critical issue is the balance of power between the federal government and the states -- an area in which Judge Roberts could move the court in either a positive or a negative direction. His work on this subject as a judge has been Delphic, raising troubling questions but not providing evidence to indicate where he would go. Senators need to satisfy themselves that he does not envision a radical departure from the past several decades of American jurisprudence on federalism.

Another subject the Judiciary Commitee will want to explore is Judge Roberts's views on privacy rights. Liberal groups have read a great deal into his work on abortion-related matters. As a government lawyer, he signed a brief urging the overturning of Roe v. Wade. In one internal memo he referred to the "so-called right to privacy." Senators should explore whether Judge Roberts, as the memo implies, has a dismissive attitude toward past decisions that protect reproductive freedom.

Along the same lines, documents from Judge Roberts's service in the Reagan administration have raised concerns about his views on civil rights issues. Some of these suggestions are unfair. However, some of Judge Roberts's memos raise questions that the Senate ought to explore. He wrote, for example, in defense of the constitutionality of legislation to strip the courts of jurisdiction to hear certain types of cases, such as abortion and school prayer, and to impose certain remedies, such as school busing. He also wrote in favor of a narrow approach to federal review of state convictions. He opposed changes to the Voting Rights Act, changes that passed Congress with broad support. He appears to have viewed affirmative action programs with deep suspicion and seemed to resist civil rights remedies that proponents had come to regard as essential to the achievement of justice. In addition, Judge Roberts's writings have been characterized as regarding decades of high-court rulings separating church and state as wrongheaded. Without revealing how he would rule on specific cases, the judge ought to be questioned on his record as a young lawyer and asked to explain where he stands now.

There is, at this stage, one major period of Judge Roberts's government career about which the Senate Judiciary Committee has seen no documents: his service as deputy solicitor general during the first Bush administration. Democrats have sought material on 16 cases; the White House has balked, citing the confidential relationship between the solicitor general's office and the government it represents. The administration seeks to protect a significant interest, but the stance is a wrong move. A procedure by which the request of the Democrats could be accommodated without seriously eroding executive prerogatives would not be hard to craft. The White House would advance the confirmation process and do Judge Roberts and itself a favor by reconsidering its position on this important question.