In a case insulating compulsory unpaid maternity leaves, the Supreme Court has been asked to decide whether a state government can do what the federal government has not done: order an interstate airline to stop compelling stewardesses to take such leaves as soon as they learn they are pregnant.

Until a few months ago, all major air carriers except Northwest Airlines enforced a mandatory-leave policy. In March, however, Ozark Air Lines settled a sex-discrimination complaint brought by the Air Line Pilots Association (ALPA) with a court-approved agreement to end the practice.

The Supreme Court case originated in 1974, when United Airlines flight attendants Linda Mortimer and Mioslawa Rosenfeld notified superiors that they were pregnant. They live in New York, one of 33 states served by United.

Under its traditional policy, which is based on "medical-safety reasons" and which is incorporated in its union contract with ALPA, United put them on leave immediately. They continued to accrue senority.

While on leave, the women filed a complaint under a New York State law making it unlawful for an employer, because of an employe's sex, "to discriminate . . . in compensation or in terms, conditions or privileges of employment."

In the State Human Rights Division, United contended that its policy is based upon an authentic safety-related occupational necessity. But the division said the evidence didn't support the contention. The Federal Aviation Administration doesn't require airlines to place pregnant stewardesses on mandatory leave, suggesting individual handling instead, the division said.

The division found that Mortimer and Rosenfeld were laid off by United without evidence that either was unable to do her job. Thus the company unlawfully discriminated against them because of their sex and owed them the wages they would have received had they been ill or disabled, the division held.

In addition, the division ordered United to let pregnant stewardesses work until their 20th week, provided a physician certifies that this wouldn't be a health or safety hazard. But if a medical exam shows a risk during the 20th to the 23th week, the company can disqualify a stewardess for further flight duty, the division said.

Last June, the state's highest court rejected, without comment, an appeal by United, which later filed a petition for review by the Supreme Court.

The petition emphasizes the case of two other United stewardesses who lived in Virginia, Karen Condit and Mary C. Oravee, and who, after becoming pregnant and being compelled to go on leave, alleged that United had violated the federal Civil Rights Act of 1964.

But U.S. District Court Judge Oren R. Levis in Alexandria, "taking into account the total pregnancy picture" at the airline, held that it was "justified" in enforcing its mandatory-leave policy because, under the 1964 act, it is a "bona-fide occupational qualification for stewardesses."

The 4th U.S. Circuit Court of Appeals affirmed last year, and the Supreme Court giving no reasons, declined in March to disturb its ruling.

In its petition for review of the New York case, United told the Supreme Court that the Human Rights Division's decision "is in direct conflict with the duty of an interstate air carrier, under federal law and as interpreted by a federal court, to operate with the highest degree of safety in the public interest."

If United now will be required to let New York-based stewardesses fly when pregnant. "there is no feasible way of allowing them to fly only in New York while pregnant," the petition said. "Thus the New York order . . . in practical effect reaches into many states and would pervade United's entire operation," although the operation requires "uniformity . . . not changes from state to state."

Replying for the rights division, attorney Ann Thacher Anderson said that the Condit-Oravec case "does not refute the division's findings that the Federal Aviation Administration, instead of requiring categorical exclusion of pregnant flight attendants from flight duty, suggests that the question of their fitness by determined case by case."