For the second time in two years, the Supreme Court yesterday rebuffed an attack on seniority systems that perpetuate the effects of past racial discrimination in employment.

The Legal Defense Fund says that the result may be to condemn hundreds of thousands of blacks to remain in the lower-paying jobs that, because of their face, had been the only ones open to them.

The case involves Ryder Truck Lines, Inc., of Jacksonville, Fla., the International Brotherhood of Teamsters, and Teamsters Local 71 in Charlotte, N.C.

In January 1973, black employes in Charlotte filed a lawsuit accusing the company, the union and the local of racial discrimination in employment in violation of both Title VII of the Civil Rights Act of 1964 and of section 1981 of a Reconstruction-era civil rights law.

The suit charged that Ryder had a consistent policy of refusing to promote or hire blacks as long-line drivers. At the time Title VII took effect, none of Ryder's long-line drivers was black. Between 1966 and 1971, the firm hired 63 long-line drivers; none was black.

The suit also charged that under the seniority system set up as part of the collective bargaining agreement with the union, black employes were locked into lesser jobs, to which they'd been assigned on the basis of race, because their accumulated seniority did not count if they were to become long-line drivers.

U.S. District Court Judge James B. McMillan agreed with the complaint. He held specifically that the seniority provisions violated both Title VII and section 1981. In 1975, the year in which he ruled, Ryder modified the seniority rules to permit transfers without loss of seniority.

The 4th U.S. Circuit Court of Appeals affirmed McMillan's ruling in April 1977. Two months later, however, the Supreme Court, in another Teamster case, ruled that Congress, in enacting Title VII, meant to uphold retirement systems that were not proved to have been adopted with a racially discriminatory intent, even if this would disadvantage persons who'd been discriminated against previously.

The question left unresolved was whether such retirement systems were legitimate under section 1981, which says that "all persons" shall have the same fundamental rights as are "enjoyed by white citizens, and shall be subject to like punishment, pains, penalties, taxes, licenses, and exactions of every kind, and to no other."

After a new hearing, the 4th Circuit modified its original decision last May to make section 1981 "co-extensive" with Title VII-meaning that a seniority system that was legal under the 1964 law also was legal under the earlier law.

In the Supreme Court, the Legal Defense Fund argued unsuccessfully that Title VII "in no manner restricted" section 1981.

By refusing the fund's plea to review the ruling, the high court left it in effect in the 4th Circuit, which includes Maryland, Virginia, and the Carolines, without resolving the issue on a national basis.