IN HIS TESTIMONY before the Senate Judiciary Committee over the past two days, Judge John G. Roberts Jr. shed important light on his views and likely approach if confirmed as the Supreme Court's chief justice. To the apparent frustration of some Democrats on the committee, he declined, as nominees traditionally do, to give his specific opinion of the merits of matters that could come before the court. But he spoke with surprising clarity on several issues and displayed an agile legal mind and an appealing ability to disagree constructively, both characteristics of a good chief justice. While Americans still lack a road map to how he will handle the many important matters the court will face, Judge Roberts is less of a sphinx than he was at the time of his nomination.

The nominee affirmed that he regards stare decisis -- the doctrine of generally allowing even erroneous past decisions to stand -- as a critical foundation of the American legal system. While he rightly pointed out that pre- cedents sometimes need to be overruled, his position distinguishes him from more radical conservatives such as Justice Clarence Thomas, who regards the doctrine as having limited value in constitutional cases. Those who might disagree with Judge Roberts's views have some assurance that he will not seek to rewrite large swaths of modern American law.

Judge Roberts made clear that he believes the Constitution contains a right to privacy, and he expressed his agreement with high- court decisions striking down bans on contraception. While he declined to address the merits of Roe v. Wade, he did indicate that it is a decision to which stare decisis considerations properly apply. Importantly, he said several times that the subsequent decision in Planned Parenthood v. Casey -- which reaffirmed Roe's core principle -- was independently entitled to be treated as a precedent. That implies that there would be a heavy burden for the court in upsetting abortion rights now. Judge Roberts was careful not to say what he would do, but his comments suggest that he appreciates the difficulty of eliminating a right the court has solemnly declared, and redeclared, in the past.

He was less clear concerning the balance of power between the federal government and the states, a subject on which his writings have been ambiguous and in some respects troubling. Still, he expressed a healthy regard for the foundations of federal power and an appreciation of the need for the courts to defer to congressional expertise. There is no reason to assume Judge Roberts will be more radical on federalism questions than either the late Chief Justice William H. Rehnquist or retiring Justice Sandra Day O'Connor.

Concerning his memos as a young lawyer in the Reagan Justice Department, Judge Roberts's answers varied considerably. He generally did not back off the substance of his memos on civil rights issues, but, rather, he stressed that the positions in question were those of the administration -- leaving ambiguous his own stance now. He did, however, retreat somewhat from his embrace of legislation to limit the jurisdiction of the courts. He also treated the court's jurisprudence on religion and public life with far greater respect than he did as a young man. His clear statement that only law, not religious faith, will govern his decisions was welcome.

The cumulative impression is of a cautious, incremental conservative, unlikely to unmask himself as a liberal once on the bench but unlikely as well to try to impose his own political agenda.