The Supreme Court banned employers Wednesday from adopting "fetal protection" policies that bar women of child-bearing age from certain hazardous jobs. The decision, calling such policies illegal sex discrimination, affects millions of working women nationwide.

The court unanimously struck down as illegal a policy of an automobile battery manufacturer banning women who cannot prove they are sterile from jobs that expose them to lead.Five of the court's nine members said sex-specific fetal protection policies never can be imposed on an employer's workforce.

"Concern for a woman's existing or potential offspring historically has been the excuse for denying women equal employment opportunities," Justice Harry A. Blackmun wrote for the court's five-member majority.

Blackmun was joined by two fellow liberals, Justices Thurgood Marshall and John Paul Stevens; Justice Sandra Day O'Connor, the court's only woman member; and Justice David H. Souter, the court's newest member.

Chief Justice William H. Rehnquist and Justices Byron R. White and Anthony M. Kennedy voted to strike down the battery maker's policy, but said the court went too far when it ruled that sex-specific fetal protection policies never could be justified as a "bona fide occupational qualification."

Justice Antonin Scalia, in a separate concurring opinion, said he generally agreed with Blackmun but seemed to suggest a fetal protection policy might be legally justified in some instances.

In other action, the court:

- Ruled that the secretary of labor, not a safety and health review board, has the last word on what federal regulations require for on-the-job safety.

- Barred Americans injured in foreign countries from suing U.S. employees based abroad.

- Overturned a $44,000 award to a nursing student who was kicked out of a Rhode Island college for being too fat.

While the case focused national attention on the rights of the overweight, today's 6-3 ruling was highly technical and did not deal directly with that issue.