WASHINGTON — Justice Sandra Day O'Connor reaffirmed yesterday she would remain on the Supreme Court until her successor is confirmed, but her presence is likely to have more symbolic than practical significance.

That is because a justice's votes really count only when an opinion is issued, not when the court first hears a case.

At first glance, O'Connor would look to be a tie-breaker for cases heard in October or November, before the Senate is likely to confirm President Bush's nominee to replace her.

But the opinions in those cases are unlikely to be issued until early next year, after O'Connor presumably would be gone. Therefore, the court could find itself evenly split 4-4.

In such instances, the justices could order that the case be reargued before the full nine-member court.

When O'Connor sent a retirement letter to the president July 1, she closed by saying her retirement would be "effective upon the nomination and confirmation of my successor." She also said she was leaving to spend more time with her ailing husband.

White House aides said Bush called O'Connor yesterday to tell her he had nominated Roberts as chief justice. In that call, she reiterated her pledge to stay on the court until Bush could win confirmation for her replacement.

Senate Democrats cited O'Connor's presence as a reason not to rush to choose and confirm a second Bush appointee.

Her presence could prove significant if the Senate were to block Bush's choice for her replacement. But if the president's nominees win confirmation by December, she is not likely to cast decisive votes.

On Oct. 5, two days after the court term begins, justices are scheduled to hear a major test of the nation's only right-to-die law. Oregon permits doctors to prescribe lethal doses of medication to terminally ill people who wish to speed their deaths.

The Bush administration has sought to nullify the law by threatening doctors with a loss of their right to prescribe medication. It relies on federal drug-control laws and argues that prescribing lethal doses is not a legitimate medical use of these drugs.

Oregon's officials and two lower courts have said the state has the power to regulate the practice of medicine.

The White House says it would like to have Roberts confirmed as chief justice by the time the court convenes, and Senate Majority Leader Bill Frist, R-Tenn., said yesterday he expected to have a confirmation vote before the full Senate by late September.

There is little chance, however, that a successor to O'Connor would also be confirmed by Oct. 3, the court's opening day.

Two days after the argument in the Oregon case, the justices will meet behind closed doors to vote. If the court splits 5-4 with O'Connor in the majority, her vote would look to be decisive.

But because the justices typically work months on their majority and dissenting opinions, the ruling probably would not be announced until early next year, presumably after O'Connor's replacement was confirmed.

In such a case, the court would be split 4-4, and would have to reargue the case if it wanted to include the new justice.