The tests for John Roberts do not really change with the decision by President Bush to nominate him as chief justice of the Supreme Court, rather than as a replacement for Associate Justice Sandra Day O'Connor. If anything, it makes Roberts easier to confirm, while increasing the stakes on the second vacancy Bush now has to fill.

The personal qualities that would have assured Roberts of a warm welcome from his colleagues on the bench -- his high intellect, work ethic, good humor and friendliness -- will serve him well as the court's presiding officer.

It is true that at 50, he is far younger than most of the justices and far junior to them as a writer of opinions, with only two years of appeals court service behind him. But he has demonstrated his literary craftsmanship in the memos from his years in the Justice Department and the White House counsel's office. The members of the court know him favorably from his many appearances as an advocate. And he is skilled enough in human relationships to show respect for his elders.

He also seems well equipped for the public role a chief justice plays as the personification of the judiciary. The man he would succeed, William Rehnquist, contributed mightily to the institution with his quiet, persistent affirmation of the independence and integrity of judges. Whether the criticism of the courts came from the left or the right, Rehnquist insisted that the judiciary be treated with respect -- and Roberts, who was his clerk and is his admirer, seems certain to maintain that vital tradition.

The relevant questions for the Senate focus entirely on his view of the Constitution and the role of the courts. Everything we know about Roberts suggests that he will be an advocate of judicial restraint, hewing closely to precedent and to a narrow interpretation of federal authority. Because of the close proximity of his views to those of Rehnquist, a court headed by Roberts is likely to function in the same centrist-conservative dimension as the Supreme Court has in recent years.

That probably spells some frustration for advocates of certain liberal causes who have come to depend on the courts to advance their agendas beyond what they can achieve at the moment in the political process. But liberals, like conservatives, need to know that lasting changes in this country must be ratified by public opinion, and the public speaks most clearly through its elected officials.

Whether an actual threat develops to established standards -- to abortion, civil liberties, civil rights, affirmative action, gender equality, environmental protections, or the separation of church and state -- probably depends on the choice Bush makes for O'Connor's replacement and Senate action on that nomination.

Because she was the swing vote on so many of these issues, where Rehnquist often found himself in dissent, it is O'Connor's seat that now provides Bush with his most significant choice.

He will be under pressure from the right wing to name someone as conservative as Roberts, or more so, to the court. Those groups that want to reverse or curtail Roe v. Wade, end affirmative action in college admissions and hiring, limit federal environmental regulation, or restore prayer to public schools and allow the public display of the Ten Commandments can sniff a possible breakthrough.

But you have to wonder how many of those issues the political side of the White House really wants to reopen to debate. Republicans are on the defensive about the war in Iraq, the handling of Hurricane Katrina, Social Security, immigration, health care and the budget. Do they really want to see a Bush-remade Supreme Court enable Democrats to blame the GOP for reversing course on abortion, civil rights and the environment?

Bush's political advisers will be conscious not only of the dangers of an ideological battle over these issues but also of the advantages of filling the O'Connor vacancy with a woman or a Hispanic judge.

Given the emphasis that Karl Rove and Bush himself have placed on courting Latino voters, it would be surprising if the president rebuffed that constituency by passing up for a second time the possibility of naming the first-ever Hispanic justice.

Many Democrats privately are convinced that Bush will choose not to miss that opportunity. They will breathe a sigh of relief if he so chooses, and happily go to war if he makes an ideological choice.