WASHINGTON – Chief Justice Rehnquist, ailing with cancer, has been hospitalized with a fever, spurring more retirement speculation about the 33-year veteran of the Supreme Court.

The 80-year-old chief justice was taken by ambulance to Virginia Hospital Center in Arlington, Va., on Tuesday night and was admitted for observation and tests, Supreme Court spokeswoman Kathy Arberg said.

There was no immediate word on his condition yesterday afternoon.

President Bush was unaware of Chief Justice Rehnquist’s hospitalization until it was publicly announced.

“We wish him a speedy recovery,” Mr. Bush’s spokesman Scott McClellan said.

Chief Justice Rehnquist’s future has been the subject of intense speculation since he announced in October that he had thyroid cancer. He has said very little publicly about his prognosis and nothing about his future at the court.

Senator Specter, who has a type of cancer involving the lymph nodes, said doctors “take extensive precautions with cancer patients who have elevated symptoms.” Mr. Specter, a Republican of Pennsylvania, is chairman of the Senate Judiciary Committee.

Justice O’Connor, 75, announced earlier this month that she was stepping down, giving the court its first vacancy in 11 years. The uncertainty about whether there will be a second vacancy has complicated the administration’s efforts to choose a replacement for Justice O’Connor.

The chief justice had been coming to the court daily but did not show up as usual yesterday morning. Court officials initially declined to say why he was absent or explain unusual happenings at Chief Justice Rehnquist’s Arlington home.

Members of the press near the residence saw a court police officer make several trips to the house, leaving each time with various personal items. First the officer carried out Chief Justice Rehnquist’s distinctive cane and a shirt. Later, he brought out other clothing.

At about 2:30 p.m., Ms. Arberg issued a two-sentence statement saying Chief Justice Rehnquist was hospitalized for a fever and was undergoing tests.

It was the second time in less than four months that Chief Justice Rehnquist was taken by ambulance to the hospital. In March, he was brought in with breathing problems. He did not stay overnight then.

Chief Justice Rehnquist has a tracheotomy tube that helps him breathe. He has been treated since October for thyroid cancer, undergoing chemotherapy and radiation. The illness led to a five-month absence from the bench, although he continued working at home and at the court during his convalescence.

The chief justice has refused to say if he plans to retire, telling reporters camped outside his house last week: “That’s for me to know and you to find out.”

Dr. Kenneth Burman, a thyroid specialist at Washington Hospital Center who is not involved in Chief Justice Rehnquist’s treatment, said it was not unusual for a cancer patient to check into the hospital with fever. “It could be a minor local infection around the tracheotomy tube,” he said.

A more serious possibility, he said, is that the cancer has spread and caused infection. Other possibilities, he said, are pneumonia, allergies to medicine, or reaction to chemotherapy.

So far, the Supreme Court has released only the barest of details about the chief justice’s health. Among the unanswered questions is whether Rehnquist has the most serious type of thyroid cancer, which is often fatal within months.