A union lawyer challenging a company's exclusion of fertile women from jobs that could harm their fetuses told the Supreme Court yesterday that upholding such restrictions would "sanction the resegregation of the work force," relegating women to second-class status in the job market.

But the company's lawyer argued that "it would violate common sense and the overriding interest in occupational health and safety to require an employer to damage unborn children."

Hearing oral argument in Auto Workers v. Johnson Controls, the court wrestled for the first time yesterday with whether "fetal-protection" policies violate federal law prohibiting job discrimination on the basis of sex or pregnancy.

The case involves Johnson Controls, a Milwaukee-based battery manufacturer that in 1982 adopted a rule barring women from jobs entailing lead exposure unless they provided medical proof of infertility.

The company said the policy was needed to protect children from severe neurological damage that can occur through prenatal lead exposure. Citing the cases of eight workers who became pregnant with elevated levels of lead in their blood despite warnings of the risk to fetuses, the company said it was necessary to ban all fertile women, not just those pregnant or planning to have chidren.

The United Auto Workers union challenged the policy, arguing that it was sex discrimination prohibited by Title VII of the Civil Rights Act of 1964 and the 1978 Pregnancy Discrimination Act.

Yesterday's argument focused on whether infertility can be a "bona fide occupational qualification," or BFOQ, a defense under federal law in cases of explicit sex discrimination. The law defines a BFOQ as a condition "reasonably necessary to the normal operation of that particular business."

If the court allows employers to adopt such policies, union lawyer Marsha S. Berzon argued, "the effect is that women will end up in the jobs where they began before Title VII was passed . . . . The net effect is that this policy, if upheld, would cut the heart out of Title VII and out of the Pregnancy Discrimination Act."

Several justices, in questioning the company's lawyer, Stanley S. Jaspan, appeared inclined to agree with that assessment.

By "considering it part of the job qualification that you not harm the fetus's health," Justice Antonin Scalia said, "it seems to me you're making a dead letter" of the Pregnancy Discrimination Act, which requires employers to treat pregnant women as they do other workers. "That was always the justification used for discriminating against pregnant women, that they shouldn't work extra-long hours because it would be bad for the fetus."

Continuing "to allow that exception is to make a farce of the Pregnancy Discrimination Act . . . ," Scalia said. "You're making it a ridiculous piece of legislation."

Justice Sandra Day O'Connor told Jaspan that "it seems to me you are not coming to grips with the effect" of the law or a case interpreting it, which "points in the direction of saying that safety concerns are not going to rise to the level of a defense under BFOQ."

But Jaspan said that "to suggest that normal operation does not include concern for health and safety would certainly be a strange notion for most manufacturers today."

Some justices also seem troubled over what level of fetal risk might justify excluding women and by whether federal judges, rather than regulators, have the expertise to assess such questions. The Occupational Safety and Health Administration, setting standards for lead exposure in 1978, did not recommend excluding fertile women.

But the justices also questioned Berzon about whether the company would be put in an unfair position if it were prohibited from adopting a fetal-protection policy and then subjected to being sued by a person who had been exposed to lead in the uterus.

Berzon discounted the legitimacy of such fears. "The fact that there's never been a case like this is itself somewhat indicative of the fact that it is not reasonably necessary to the normal operation of the business for an employer to turn somersaults in order to avoid a theory of liablity that does not yet exist," she said.