The Supreme Court yesterday upheld seniority systems that perpetuate past employment discrimination against blacks, Hispanics and women.

The court acted in a case involving the unionized over-the-road trucking industry and in a separate case involving airline stewardesses.

In yet another labor matter, the court ruled that a state can deny unemployment benefits to a worker who is laid off because of a dispute somewhere else between his employer and a union.

The justices voted 7 to 2 to uphold the senority system in the trucking case on the ground that the International Brotherhood of Teamsters negotiated and maintained it free of discriminatory intent.

But the court said the system allocates "the choicest jobs, the greatest protection against layoffs, and other advantages to those employees" who have "line" - over-the-road - drivers for the longest time. Nearly all the time drivers are white.

At the same time, the justices voted unanimously to strike down a prevalent industry practice, the "no transter" drule, that requires local drivers predominantly blacks and Hispanics to forfeit all of their senority merely to apply for jobs as line drivers.

The case evolved from a 1971 government suit against T.I.M.E. - D.C. Inc. of Lubbock. Tex. a nationwide trucking firm, and the Teamsters, which represented a large proportion of its 6.472 employees.

In the opinion for the court, Justice Potter Stewart said the government had proved that the company engaged system-wide in a pattern or practice of employment discrimination in violation of the Civil Rights Act of 1964.

Statistics and testimony both showed that the firm regularly and purposefully discriminated against blacks and Hispanics particularly in regard to line driving jobs, the court said.

Of 1,828 line drivers, for example, the minorities accounted for only 13 - all hired after the government sued. One black worked as a line driver from 1950 to 1959. After that, none did, so a regular basis, until 1969.

Stewart wrote about men who "brought the cold numbers convincingly to life."

One, George Taylor, a black who was a city driver in Los Angeles, expressed an interest in becoming a line driver in 1968. The terminal manager foresaw "a lot of problems. . .with different people. Caucasian, etc.," and said, "I don't feel the company is ready for this right now. . . Give us a little time." Taylor made similar requests later and got similar answers - but never got the job or even an application form.

In T.I.M.E.'s Denver terminal, dockman Feliberto Trujillo was told by a personnel officer in 1967, when he applied for a job as a line driver, that he had one strike against him: "You're a Chicano. . ."

While men such as Taylor and Trujillo were being rejected, the company was hiring hundreds of whites as line drivers, from both inside and outside the ranks.

Because such discrimination persisted even after the Civil Rights Act became effective in July, 1965, the justices ruled that a lower court to which they returned the case may award retroactive senority to the victims, even though the senority system makes no provision for such relief.

The high court also presumed that every black and Hispanics who applied to be a line driver is entitled to relief, and that employees who can prove they would have applied but for discrimination also are presumptively entitled to retroactive senority.

The Fifth U.S. Circuit Court of Appeals had agreed with the government's contention that any senority system perpetuating past discrimination can never be "bona fide" under the civil rights law. Nullifying that ruling, the Supreme Court said Congress' "unmistakable purpose was to make clear that the routine application of a bona fide senority system would not be unlawful. . ."

Justice Thurgood Marshall, in a dissent joined by Justice William J. Brennan Jr., accused the majority of a "radical reconstruction" of congressional intent.

In more than 30 cases, they said, six unanimous courts of appeal have held that the law does not immunize senority systems that perpetuate the effects of prior discrimination. Similarly, they said, the Equal Employment Opportunity Commission reached the same conclusion "in an unbroken line" of more than 20 cases since 1969.

Over the years, senority systems neutral on thir face have become controversial partly because they sometimes operate against women. If they are the last hired, for example, they are the first furloughed when jobs become scarce.

Another case decided yesterday, with the same dissenters, involved Carolyn J. Evans, a United Air Lines flight attendant for 16 months until February, 1968. She was forced to resign because she got married while UAL had a rule requiring stewardesses to be single. She returned to work four years later, 3 1/2 years after a collective bargaining agreement abolished the rule. Denied reinstatement, she came back as a new employee with no senority credit.

In the opinion for the court reversing the Seventh U.S. Circuit Court of Appeals, Justice John Paul Stevens said the senority system had not been intentional designed to descriminate against women.

In the unemployment benefits case, the court voted 8 to 0 to uphold the constitutionality of an Ohio law that disqualified Leonard P. Hodory, a United States Steel Corp. employee in Youngstown, who was furloughed when his plant ran out of coal. The coal ran out because of a United Mine Workers strike at distant mines.