Nathalie Norris learned in 1975 that it was not entirely a blessing that women tend to live longer than men.

Norris signed up that year for a private annuity plan sponsored by her employer, the state of Arizona, only to discover that upon retirement she would receive lower benefits per month than her male counterparts.

The state would deduct $199 a month from both men's and women's paychecks, according to the plan, but would pay $34 per month less to the women when they retired. Over 20 years, the difference would be about $8,100.

The reason for the discrepancy is the widespread and time-honored insurance industry practice of calculating insurance costs by sex. Norris' monthly benefits were being stretched out to last longer because she was a woman and, it was assumed, would live longer.

Yesterday, Norris' lawyer, Amy Jo Gittler, asked the Supreme Court to declare the practice illegal under federal civil rights law. It violates the law, Gittler told the justices during an hour of oral argument, for an employer to dispense fringe benefits according to race, national origin or, as in this case, gender.

Norris' case challenges the use of such benefit schedules by employers. Congress is considering legislation that would go further and make sex-based actuarial tables illegal for the entire insurance industry, a step that insurance officials say would revolutionize their business and cost millions of dollars.

Not since the controversy during the '60s and '70s over no-fault insurance has the industry been so aroused by an issue. Its concern is shared by employers, like the state of Arizona, who say they believe that employer-funded retirement and insurance programs might be bankrupted by a negative ruling, particularly by a retroactive decision, forcing them to equalize benefits for millions of women already covered.

The court challenges are based on Title VII of the Civil Rights Act of 1964, which makes it illegal for employers to discriminate on the basis of race, sex or national origin.

The annuity plan, said Gittler, "cannot be based on statistics. We must look to individuals. We must treat individuals as individuals, not as group statistics."

Nathalie Norris, she said, "is receiving less from month to month" than a man would in her situation. Arizona is "providing a discriminatory fringe benefit to its employes," she said, in what she said is clear violation of Title VII.

Arizona's annuity plan is one of several options offered to state employes under a deferred compensation program. The others include retirement plans that pay a lump sum to everyone without distinguishing between men and women. While offered through the state, the program is handled by an insurance company hired by the state.

John L. Endicott, arguing for Arizona yesterday, said that the private insurance company is responsible for the sex-based retirement plan, not the state. The state had little choice, he said, since most companies base their calculations on the same mortality tables.

"The employers are not responsible for the fact that the insurance market treats women differently than men," he told the justices. The women "are using Title VII to punish employers for what the insurance industry has done."

Endicott's argument is crucial to the case, since there is no law under which the women could sue the insurance companies.

Endicott also said he thought the issue was "a social and political problem, for the legislatures and the Congress." A court ruling, he said, "may bankrupt and render insolvent a lot of employer-funded plans."

Gittler argued that the practice was found to be illegal in a 1978 Supreme Court case, City of Los Angeles Department of Water & Power vs. Manhart. In that case justices held that a city pension plan was illegal because women had to make higher payments into it than men. The court said civil rights law "precludes treatment of individuals as simply components of a racial, religious, sexual or national class." The Los Angeles case did not involve an outside insurance company, however.

The case nevertheless was cited by the 9th U.S. Circuit Court of Appeals when it ruled in Norris' favor in yesterday's case, Arizona Governing Committee for Tax Deferred Annuity and Deferred Compensation Plans et al vs. Nathalie Norris. Two other recent appeals court rulings also have sided with women on the issue, while another has favored insurers.

Justice John Paul Stevens asked yesterday whether the state could solve the discrimination problem by eliminating the offending annuity plan.

"That is always a possibility," Gittler responded. "Employers can always evade their responsibility by eliminating all their employes."

Chief Justice Warren E. Burger asked whether it is also illegal for women to be charged lower premiums for life insurance because of their longer life spans.

"Yes," Gittler said, "if it is in the context of an employer-sponsored plan."