In a ruling that could force a delay in the Texas primary, now less than a month away, the Supreme Court said yesterday that a three-judge panel improperly imposed a congressional redistricting plan on the state last February.

The panel had rearranged the plan of the Texas legislature, saying it was a "severe retrogression" for minorities in the city of Dallas. But it stopped short of finding the legislative plan illegal or in violation of the Constitution.

The justices, in an unsigned opinion issued yesterday without dissent, said that the panel overstepped its authority. "In the absence of a finding that the Dallas reapportionment plan offended either the Constitution or the Voting Rights Act," the justices said, "the District Court was not free, and certainly was not required, to disregard the political program of the Texas State Legislature."

Yesterday's decision was sought by U.S. Solicitor General Rex L. Lee, on behalf of the Justice Department, and by officials of the Republican Party in Texas, which fared better under the legislative plan.

The question now is whether there is sufficient time before Texas' May 1 elections to readjust boundaries, candidates and campaigns in light of yesterday's action. The justices left the lower court free to readjust before or after May 1. In either case, the legislature's plan would be restored for the next election.

Democratic officials in Texas said it would be impossible to go back to the legislative plan and still hold the primary May 1, but Republicans disagreed.

State GOP officials, who greeted the decision with glee, said they would ask the court to restore the legislative plan, allow candidates one additional day to file, and hold the primary as scheduled. But they indicated that they would rather delay the primary, possibly until June 5, than hold elections under the judicial plan struck down yesterday.

The judicially imposed plan had overturned an attempt by Republicans and some minorities in the Dallas area to create a new minority district, in the process eliminating a safe Democratic seat.

The judges also redrew the boundaries between two south Texas districts that had been criticized by the U.S. Justice Department as violating the Voting Rights Act.

"The only limits on judicial deference to state apportionment policy," the justices said yesterday, are statutory and constitutional requirements. If those are not found to have been breached, courts must "defer to the legislative judgments," the Supreme Court said.