The Supreme Court ruled 6 to 2 yesterday that a pension plan cannot make women pay more than men for the same retirement benefits simply because the average woman lives longer than the average man.

An employer-operated pension fund that requires unequal contributions from men and women violates the ban in the Civil Rights Act of 1964 on "treatment of individuals as simply components of a racial, religious, sexual, or national class," the court held.

At least by implication, the court also struck down a more common type of plan in which the pay-in equal but the pay-out for women is lower.

Retirement systems other than Social Security enroll 50 million Americans, but most of them - including employes of the federal government and employes of private firms in plans negotiated by unions - will be unaffected because their plans are sex-neutral.

However, the decision will have a major impact on plans covering teachers and other employes of state, county and municipal governments. In New York City alone, such plans cover more than 300,000 teachers.

The court ruled in a case brought by five women employes of the Los Angeles Department of Water and Power and by their union, Local 18 of the International Brotherhood of Electrical Workers, AFL-CIO.

Relying on standard mortality tables and its own experience, the department determined that, on the average, its 2,000 female employes will live a few years longer than its 10,000 male employes.

That calculation meant that the average woman would draw more monthly retirement payments than the average man. Consequently, the department set the payroll deduction for women 14.84 percent higher than for men.

Before retiring, one woman paid in $18.171 including interest. A comparable man would have paid in $5,328 less.

A state law enacted while the case was pending barred the water and power department and other municipal agencies from requiring larger pension-fund contributions from women. As a result, the department plan was revised to be general-neutral as of Jan. 1975.

Nonetheless, a U.S. District Court judge and then the 9th U.S. Circuit Court of Appeals ruled the old plan violated Title VII of the 1964 civil rights law.

In the Supreme Court ruling affirming the lower courts, Justice John Paul Stevens emphasized the law bars discrimination against "any individual . . . because of such individuals" sex or other individual characteristics.

"If height is required for a job, tall womam may not be refused employment merely because, on the average, women are too short," Steven said.

In the Los Angeles case, it was of "critical importance" that there was "no assurance that any individual woman working for the department will actually fit the generalization on which the department's policy [was] based," he said.

Stevens acknowledged that male employes now may be subsidizing women, to some extent. But he cautioned against sweeping interpretations of acturial tables, noting, for example, that "a significant part" of the greater longevity attributed to women "may be explained by the social fact that men are heavier smokers."

Rejecting the department's claim that equality in pay-in is unfair, he said. "When insurance risks are grouped, the better risks always subsidize the poorer risks.

"Healthy persons subsidized medical benefits for the less healthy; unmarried workers subsidize the pensions of married workers; persons who eat, drink, or smoke to excess may subsidize pension benefits for persons whose habits are more temperature," Stevens said.

He noted a study showing that it divorced, 20-year-men could expect to live to age 60.6, while if married they could expect to live to 70.9.

Jonining Stevens in the opinion for the court were Justices Potter Stewart, Bryon R. White, Thurgood Marshall and Lewis F. Powell Jr. Justice Harry A. Blackman joined only in the result, Justice William J. Brennan JR., ill when the case was considered, did not participate.

Chief Justice Warren E. Burger, joined by Justice William H. Rehnquist, dissented. Burger found it "irrational to assume Congress intended to outlaw use of the fact that, for whatever reasons of combinations of reasons, women as a class outlive men."

To recognize greater female longevity is not a failure to treat them as individuals, Burger said. "It is to treat them as individually as it is possible to do in the face of the unknowable length of each individual life," he said.

With only Marshall dissenting, the justices reversed the lower courts' award of retroactive compensation to the Los Angeles department's women employes.

"Retroactive liability could be devestating for a pension fund" with the bill failing largely "on innocent third parties" Stevens said. Marshall termed the sum involved "modest" and the possibility of harm to the innocent "largely chimerical."