Chief Justice William H. Rehnquist is being treated for thyroid cancer at the Bethesda Naval Hospital, the Supreme Court said today.

A statement from the court said Rehnquist, 80, is expected to return to the bench on Nov. 1.

He was admitted Friday, the court said, and underwent a tracheotomy, a surgical procedure in which an opening is created in the throat to aid in breathing. The statement did not say why he had the tracheotomy.

Many forms of thyroid cancer are treatable, depending on the type, the stage and the age of the patient.

That did not stop a frenzy of speculation on television news programs about possible successors to Rehnquist and the possible impact of a Rehnquist departure on the election. Because of the advanced age of some of the justices, it is generally assumed that two or three or more will depart during the term of the next president.

Rehnquist, a Milwaukee native who practiced law in Phoenix, was appointed to the court in 1972 by President Richard M. Nixon. He had served as deputy attorney general in the Nixon administration.

President Reagan appointed him chief justice of the United States in 1986, following the retirement of Warren E. Burger.

Throughout his tenure, Rehnquist has been considered among the most conservative justices ever on almost every major social issue confronted by the high court.

Thyroid cancer is diagnosed when malignant cells are found in the tissues of the thyroid gland at the base of the throat.

"The problem with thyroid cancer is that it represents about half a dozen different diseases," said Paul Wallner, an expert at the National Cancer Institute. "Some of them are highly curable and quite low grade and can be treated without massive intervention," he said.

"The most common type is what we call the well-differentiated lower grade" thyroid cancer, said Wallner. "Those are highly treatable and highly curable. They tend to occur in a slightly younger age group," he said. "I worry about any 80 year old with any illness."

Treatment generally involves surgery to remove the cancer and sometimes follow up radiation therapy. "The thyroid is readily accessible and is not in an area of the body that undergoes the stresses of the abdomen or chest," Wallner said. "People who have thyroid surgery can sometimes return relatively quickly," to normal life, Wallner said.

Asked about the tracheotomy, Wallner said the "issue is whether he had the tracheotomy for purposes of neck surgery" to remove the cancer, which is temporary and routine, or whether he had it because he was having trouble breathing.

Breathing problems "would suggest that a mass may have been more extensive," Wallner said, and that the tracheotomy might need to remain in place longer.

Wallner stressed that he had no specific knowledge about Rehnquist's situation.

The last vacancy on the court occurred in 1994, and then-President Bill Clinton appointed Stephen Breyer to fill the seat vacated when Justice Harry M. Blackmun retired.

Other members of the high court have also been treated for cancer. Justice John Paul Stevens, the oldest at 84, has had prostate cancer. Justice Sandra Day O'Connor had breast cancer and Justice Ruth Bader Ginsburg had colon cancer.