HIV-infected people are protected by a federal ban on discrimination against the disabled even if they suffer no symptoms of AIDS, the Supreme Court ruled Thursday.

The 5-4 ruling ordered a lower court to reconsider whether a Maine dentist violated the Americans With Disabilities Act when he refused to fill an HIV-infected woman's tooth in his office."HIV infection satisfies the statutory and regulatory definition of a physical impairment during every stage of the disease," Justice Anthony M. Kennedy wrote for the court.

The justices said the dentist involved in Thursday's case, in deciding how to treat an HIV-infected woman, "had the duty to assess the risk of infection based on the objective, scientific information available to him and others in his profession," Kennedy wrote.

In deciding whether a health-care provider has violated the disability-protection law, "courts should assess the objective reasonableness of the views of health-care professionals without deferring to their individual judgments," the justice said.

Thursday's ruling set aside a lower court decision that said dentist Randon Bragdon violated the anti-discrimination law when he refused to fill Sidney Abbott's tooth in his office because she carries the virus that causes acquired immune deficiency syndrome.

The justices instructed the lower court to reconsider the case under Thursday's ruling. Kennedy added, "We do not foreclose the possibility that the Court of Appeals may reach the same conclusion it did earlier."

The ADA, signed by President George Bush in 1990, protects the disabled against discrimination in jobs, housing and public accommodations such as dentists' offices. Some of the law's most visible results are aids such as wheelchair ramps at countless public places.

The law says people are disabled if they have a physical or mental impairment that "substantially limits one or more major life activities."