ASHINGTON, Nov. 6 - A Supreme Court with an absent and ailing chief justice is very different from a White House with an absent and ailing president. While the president embodies one entire branch of government, the chief justice merely heads another.

In the two weeks that Chief Justice William H. Rehnquist, 80, has been treated for a serious form of thyroid cancer, life at the court has proceeded without a sense of crisis. The judicial function is shared by eight other people, with Justice John Paul Stevens, the senior associate justice, presiding over courtroom sessions and the justices' private conferences. The administrative tasks are carried out, as they usually are under the chief justice's direction, by his administrative assistant, Sally M. Rider, a former federal prosecutor and State Department lawyer.

These arrangements can continue almost indefinitely. Nonetheless, as it has become evident that Chief Justice Rehnquist will not be returning soon, a sense of sadness and uncertainty has spread throughout the court and into the wider community of federal judges who have received no more information than the general public about the chief justice's condition and prospects.

Judges have refrained from calling either Chief Justice Rehnquist or Ms. Rider. "I don't have the nerve," one judge who has worked closely with the chief justice said Friday. "The vibes I get just aren't good."

A judge who did call the chief justice's chambers in anticipation of a visit to Washington was steered away from visiting his home in Arlington, Va. The justices have sent notes, but it is not clear whether any have seen or even talked to him.

Information from official channels has been minimal. The court's press office would not say whether the chief justice was present for the justices' regular Friday morning conference, at which they review new cases and decide which to grant. (He was not.) Nor would the press office say whether, if he did not attend, he sent in his votes. (He did.)

The chief justice, it appears, has functioned as his own press officer. Surely a professional would have cautioned him, on the day it was announced that he had just undergone a tracheotomy, against making a public promise to be back at work in a week. Every cancer specialist whom reporters consulted after the announcement found that prediction highly implausible.

And when the chief justice found on Monday that he could not fulfill the promise, he subtly but unmistakably indicated that the error had been his own and not his doctors': "According to my doctors, my plan to return to the office today was too optimistic."

Chief Justice Rehnquist's statement on Monday said that he was receiving radiation and chemotherapy on an outpatient basis. Both the aggressive treatment and the observations of those who have seen him in recent weeks suggest that the disease is advanced and rapidly progressing.

A judge who attended a meeting with him in late September said the chief justice looked well and spoke without the hoarseness that was apparent by the time the court's new term began Oct. 4; a spreading thyroid tumor can impinge on the nerves that control the vocal cords. By mid-October, one court employee who saw the chief justice in his street clothes was struck by his frailty. "That robe can hide a lot," this employee said.

The court will hear arguments in this coming week and then again in the two weeks following the Thanksgiving weekend. It will then go on recess until Jan. 10. During that substantial interval, people at the court now appear to think, the chief justice will have a chance to assess his situation and decide whether to retire.

Although there seems to be widespread public confusion on this point - memories have faded in the 18 years since Chief Justice Rehnquist's contentious confirmation hearing - a chief justice must be separately nominated by the president and confirmed by the Senate, even if the person is already sitting on the Supreme Court. If the president wants to choose a sitting justice, he can pick any of them, without regard to seniority.

Historically, promotion from within has been the exception; only 5 of the 16 chief justices previously served as associate justices, including Chief Justice Rehnquist, who spent his first 14 years on the court as an associate before President Ronald Reagan offered him a promotion in 1986.

The timing of his illness, more than two months before the start of the 109th Congress, raises another prospect: that of a recess appointment to the court. The Constitution gives the president the power to make appointments to fill "vacancies that may happen during the recess of the Senate," although whether and under what circumstances this authority applies to judges is open to some debate.

A case recently appealed to the Supreme Court on which the court could act as early as Monday challenges the validity of President Bush's appointment of William H. Pryor to a federal appeals court during an 11-day Congressional recess last February.

A recess appointment expires at the end of the following session of Congress unless confirmed by the Senate in the interval - in late 2005 for any appointments made in the remaining weeks of 2004, or at the end of the second session of the new Congress, in late 2006, for appointments made after Jan. 1.

While there have been 12 recess appointments to the Supreme Court, 9 of them occurred in the early years of the country. The only 3 recess appointments in modern times, those of Chief Justice Earl Warren and Justices William J. Brennan Jr. and Potter Stewart, were all made by President Eisenhower in the 1950's.

Although the Senate subsequently confirmed those three justices, the experience left many senators uneasy. While some simply resented the exercise of presidential power, others argued also that judicial independence was compromised by the recess-appointed justices' knowledge that they would be confirmed to lifetime appointments only if the Senate was satisfied with their performance.

In 1960, the Senate passed a resolution opposing the practice on a largely party-line vote, with most Democrats voting for the resolution and all the Republicans opposed.