The Supreme Court yesterday significantly broadened federal sex discrimination laws by expanding the obligation of employer health insurance plans to cover the pregnancy costs of workers' wives.

The court, in a 7-to-2 ruling, said that employers who fully insure spouses for other medical needs cannot deny or limit pregnancy coverage for them. The practice, a money-saving approach for many businesses, discriminates against male employes by giving them less comprehensive coverage than their female co-workers, the justices said.

Yesterday's decision, vigorously opposed by industry groups, could cost businesses millions of dollars in increased insurance costs.

Officials of the Equal Employment Opportunity Commission, which sought the ruling, said that virtually the entire railroad industry and many other firms, particularly in the South, engage in the practice declared illegal yesterday.

The Pregnancy Discrimination Act, passed in 1978, already protects female employes from discrimination in insurance coverage when they become pregnant. The question yesterday, which had divided the lower courts, was whether that amendment to the Civil Rights Act of 1964 also protects spouses of male workers.

The case arose from a male employe's complaint against the Newport News (Va.) Shipbuilding and Dry Dock Co. The firm fully insured female workers for pregnancy and fully covered spouses for most medical needs. But it covered only a portion of the childbirth costs for the wives of its male workers, placing a $500 limit on hospital charges. Those charges, separate from delivery and anesthesiology fees, can soar to thousands of dollars for complicated deliveries.

Justice John Paul Stevens, writing for the court, said that Congress enacted the 1978 law to make sure that employers treated pregnancy no differently from any other medical condition.

Under the Newport News plan, he wrote, "the husbands of female employes receive a specified level of hospitalization coverage for all conditions" while "the wives of male employes receive such coverage, except for pregnancy-related conditions."

Congress, he said, "has unequivocally rejected that reasoning." The insurance plan at issue "unlawfully gives married male employes a benefit package for their dependents that is less inclusive than the dependency coverage provided to married female employes," Stevens wrote.

EEOC lawyer Ruth Weyand said yesterday that her agency has about 50 complaints against different companies that were riding on the decision in Newport News Shipbuilding & Dry Dock Co. v. EEOC. She also said that the opinion may have broader implications when it is applied to disputes involving other fringe benefits, such as legal insurance or home insurance. Such benefits are increasingly a part of employe compensation, she said.

In 1976, the Supreme Court ruled in General Electric Co. v. Gilbert that federal anti-bias law (Title VII) does not require companies to insure female workers for pregnancy, even when they cover all other health needs of employes.

The Pregnancy Discrimination Act was designed to overrule that holding.

Justice William H. Rehnquist, joined by Justice Lewis F. Powell Jr., dissented yesterday, saying that the court had misread the 1978 law. "Nothing in the Pregnancy Discrimination Act even arguably reaches beyond female employes affected by pregnancy," they said.

In another ruling yesterday, the court upheld the practice of having trained dogs sniff luggage at airports in search of drugs. But the justices said that authorities are limited in the amount of time they may hold luggage for this purpose.

The decision was one in a series giving federal officials broad authority to combat drug smuggling. Last week, the justices upheld the power of customs officials searching for drugs to board boats and ships on rivers and channels with easy access to the open sea.

Yesterday's case, U.S. v. Place, began at Miami International Airport when police grew suspicious of Raymond J. Place, who was boarding a flight to New York. They asked to see his identification and his airline ticket. They also asked for--and received--permission to inspect his luggage, which had been checked.

Because his flight was about to depart, they did not search the luggage. Instead, they notified Drug Enforcement Administration agents in New York, who intercepted Place at LaGuardia Airport and seized his luggage.

Since there were no trained dogs at LaGuardia, the luggage was transferred to Kennedy International Airport, where it was held for 90 minutes for the canine sniff, which was positive.

Police then obtained a warrant to open the bags and found 1,125 grams of cocaine.

The 2nd Circuit U.S. Court of Appeals said that the prolonged seizure of the luggage was unconstitutional because police did not have "probable cause" to suspect criminal activity by Place.

Justice Sandra Day O'Connor, writing for the court, said that a canine sniff may be justified by the mere suspicion of wrongdoing, something less than probable cause. But 90 minutes was too long to hold the luggage, she wrote, agreeing that the evidence must be thrown out. Previous decisions that forbid holding an individual that long under similar circumstances also bar such a prolonged seizure of the luggage, she said.

Justices William J. Brennan Jr., Harry A. Blackmun and Thurgood Marshall agreed that the evidence must be thrown out because of the prolonged seizure of the luggage. But they also said O'Connor went too far in allowing the canine sniff without probable cause. Previous Supreme Court rulings "do not provide the police with a commission to employ whatever investigative techniques they deem appropriate," Brennan wrote.