A three-judge federal panel today ordered the May 1 Texas primary to be held as scheduled on the basis of a redistricting plan recently invalidated by the Supreme Court.

In a split decision hailed by the Democratic Party, the judges said there was not enough time between now and election day to reinstitute a redistricting plan adopted last year by the Texas legislature without causing disruption to both candidates and voters.

Republican Party officials, who had asked the court to hold the May 1 elections under the plan approved by the state legislature, said they would file an immediate appeal to the Supreme Court.

As a result of today's ruling, congressional redistricting will be tossed back to the legislature when it convenes next January.

In oral argument today, all parties urged the court to order the primary election to be held on May 1, as scheduled.

But the Republicans argued that there was sufficient time to return to the lines drawn last year by the legislature, while the attorney for the plaintiffs and the Texas Democratic chairman urged the court to use its plan on an interim basis this year, as allowed by the Supreme Court in its ruling.

The congressional redistricting plan that will be in effect for the 1982 elections was drawn in February by the three-judge panel after minority groups challenged the legislature's plan in court, saying it diluted minority voting strength.

The Justice Department found in January that the legislature's plan violated the Voting Rights Act in two south Texas districts, but found no violations in the Dallas area.

The three-judge panel, however, found "severe retrogression" for minorities in the Dallas area, and on that basis redrew the lines in four congressional districts there.

But the court-ordered plan was struck down last week by the Supreme Court, which ruled that the three-judge panel had redrawn the lines in the Dallas area without finding a constitutional or Voting Rights Act violation.

In effect, said the Supreme Court, the judges had improperly substituted a plan of their own for one approved by the legislature.

The plan approved last August by the legislature was considered a Republican plan. It created a minority-dominated district in Dallas and in the process turned the now-Democratic 5th District into a Republican stronghold.

The boundaries drawn by the three-judge panel divided the minority vote more evenly between the two adjacent districts and was considered favorable to the Democrats.

Although the Supreme Court said the lower court plan should be invalidated, it left to the three-judge panel the decision on how to proceed for this year's elections.