Chief Justice William H. Rehnquist's (search) health is shrouded in mystery, the extent of his thyroid cancer a closely guarded secret. Several coming events could give the public an idea about the seriousness of his condition.

Since announcing his illness in a statement on Oct. 25, the 80-year-old Rehnquist has run the nation's highest court from his home in suburban Virginia.

He rules on cases by reviewing transcripts of arguments and passing along his votes to justices. Opinions are largely researched and drafted by law clerks. Administrative tasks fall to a top aide.

The only update on his condition came in a short statement from the court three weeks ago. It said he was receiving chemotherapy (search) and radiation treatments, which some doctors familiar with thyroid cancer said suggests Rehnquist has a fast-growing cancer.

Speculation about whether he will step down and give the court its first opening since 1994 has swirled since disclosure of the illness. Three events could offer telling signs of Rehnquist's future after nearly 33 years on the high court, the last 18 as chief justice.

— The return of the court, which next hears arguments on Nov. 29.

— The annual court Christmas party on Dec. 17, an event Rehnquist relishes.

— President Bush's inauguration on Jan. 20. The chief justice (search) normally swears in the president. Bush could choose another justice or other government official.

The court can function indefinitely without a chief justice; the only constitutionally required duty is to preside over a presidential impeachment trial. But the pressure on Rehnquist to disclose his plans will become too great for him to remain silent, predicted David J. Garrow, a law professor at Emory University and Supreme Court historian.

"I don't think things will stay in abeyance beyond January," he said.

The Supreme Court has operated with minimal disruption up to now. The next several weeks, however, will be critical as the ailing chief justice who prides himself on keeping the trains on time ponders whether he can keep up, said Pepperdine University law professor Douglas Kmiec.

Rehnquist has missed every argument since mid-October, so if he is not on the bench when the court returns in a week, it will not be terribly noticeable.

More significant may be the Christmas party for court staff that Rehnquist hosts each year. He makes meticulous plans, from the smallest of tree trimmings to leading a round of Christmas carols that he insists all attendees join.

But the most significant — and most public — absence would be if Rehnquist is unable to swear in Bush. By then, Rehnquist should have completed most of his treatment and will have had time to fully assess his health and whether he is able to continue on the court.

If he does not appear, it would be only the ninth time the chief justice did not administer the oath. The last time was Nov. 22, 1963, when a U.S. district judge swore in Lyndon Johnson on Air Force One after President Kennedy's assassination.

"The inauguration is an enormously important ceremonial statement for the nation and world," said Kmiec, a former legal counsel to President Reagan and the first President Bush. "To not have him present at that moment would convey the significance of his absence."

If Rehnquist delays a decision on his future past January, it would make it very difficult for a Bush nominee to win confirmation in time to sit for arguments, which end in April.

If Rehnquist becomes unable to cast votes, it could severely effect the court. Tie decisions would uphold the lower court's ruling. Those decisions, however, would only be binding within that lower court's jurisdiction.

Several court watchers and former clerks say that Rehnquist is not one to stick it out any longer than he feels able. They noted that he was a witness to Justice William O. Douglas' steady decline after a stroke in December 1974.

Douglas' refusal to step down despite obvious mental confusion led Rehnquist and the other justices to secretly stop counting his vote in some cases. Douglas eventually stepped aside in 1975.

"If and when he concludes he cannot come back, the chief justice will send his letter to the president immediately," Garrow said.