Chief Justice William H. Rehnquist was taken to Virginia Hospital Center in Arlington yesterday after developing a fever, marking the second emergency visit in the past month by the jurist, who has cancer. Rehnquist, 80, who vowed just three weeks ago to keep working "as my health permits," was admitted for "evaluation" and allowed to go home, according to Supreme Court spokesman Ed Turner.

Court officials declined to provide further details. Rehnquist has been undergoing treatment for thyroid cancer since November. He spent two nights at the same hospital last month, also after developing a fever.

His latest visit to the hospital comes amid a fierce political struggle on Capitol Hill over appellate court judge John G. Roberts Jr., who has been nominated by President Bush to succeed retiring Supreme Court Justice Sandra Day O'Connor.

Rehnquist has long guarded his privacy, and has declined to reveal details about his illness. It was diagnosed in October and resulted in radiation and chemotherapy treatment in November.

Doctors not connected to his case have said that fever-producing infections are common in patients who, like the justice, have a surgical opening in their throat to permit breathing. The opening increases the risk of infection in the lungs, bronchial tubes and trachea.

Rehnquist resumed work in December and administered the oath of office at Bush's inauguration. He presided over oral arguments in the spring and has continued to work at the court this summer, hiring three law clerks for the term that will begin in October. Officials said Rehnquist worked at the court earlier yesterday.

After his July 14 release from the hospital, Rehnquist issued a statement denying any intention to step down. "I want to put to rest the speculation and unfounded rumors of my imminent retirement," Rehnquist's statement said. "I will continue to perform my duties as long as my health permits."

His symptoms and reported course of treatments have led many outside experts to speculate that Rehnquist may be suffering from anaplastic thyroid cancer, which leaves most of its victims dead within a year of diagnosis. But Rehnquist's emphatic statement last month and his continued work at the court have led others to believe the disease may be less aggressive.