The full U.S. Court of Appeals here has voted to rehear two cases challenging affirmative action plans for the D.C. police and fire departments. Separate three-judge panels have upheld the police department's plan and overturned the fire department's.

The decision to hear the cases en banc, or by the full court, will delay for at least a year final resolution of the lawsuits, which already have tied up some hiring and promotions in the two departments for as long as five years.

The fire department case has attracted national attention because the Reagan administration has made it a centerpiece of its campaign to eliminate racial quotas in the public sector.

The hearing before the full court, set for May 4, will be limited to questions raised by the Supreme Court's landmark decision last March, which held that employers may use affirmative action plans to promote women and minorities ahead of white males even if there has been no evidence of prior discrimination.

The judges ordered the attorneys in both cases to focus on constitutional questions and several procedural matters and scheduled the two cases to be heard during the same proceeding.

In a split decision in February, a three-judge panel of the court threw out the fire department's affirmative action plan specifically on the grounds that there was no showing of prior discrimination. Six months later, the panel refused to reconsider its decision, saying that the Supreme Court's decision was narrow and did not apply to the D.C. plan.

Several lawyers involved in the two cases said yesterday that they had not been notified that the full court has voted to review the cases.

"We are very pleased," said Joel Bennett, an attorney for 21 police officers in their reverse discrimination case, Ledoux v. District of Columbia, and had asked for the full court hearing. "We look forward to arguing the case."

Beverly Burke, spokeswoman for the D.C. corporation counsel, said that she had no comment on the court's decision to review the police case. However, she said her office was "very glad" about the decision in the firefighers' case, Hammon v. Barry.

Attorneys representing city firefighters could not be reached for comment last night.

Two groups, one representing white firefighters and the other representing blacks, are involved in the Hammon suit, and both opposed the department's affirmative action plan, but for different reasons.

The Progressive Firefighters Association, which filed the Hammon suit on behalf of two black firefighters, opposed the plan on the grounds that it did not go far enough to correct discriminatory practices. Specifically, the black firefighters objected to the city using an entrance examination that had not been validated to be free of bias.

Local 36 of the International Association of Fire Fighters opposed the plan, saying it was reverse discrimination.

City officials, who agreed to the affirmative action plan as part of a consent decree, have severely criticized the Reagan administration for intervening in the case.

The hiring provisions of the fire department's plan were approved by U.S. District Judge Charles R. Richey in April 1985, but he threw out the promotion part of the plan. The hiring plan in the case expired in April, but Richey has been overseeing development of a new plan, which likely will be deferred pending the outcome of the full court review.

The police affirmative action case has received less attention. It was brought in 1982 by 21 whites who held the rank of detective II and claimed they were discriminated against when they were passed over for promotion to detective I four years earlier.

The officers, all of whom had been rated "exceptionally well qualified," argued that there were irregularities in the promotion process because three black men, one white man and a white woman were added to the list of promotions by the police chief after the normal process was completed.

U.S. District Judge John Garrett Penn upheld the promotions in May 1986, 2 1/2 years after the trial. A three-judge panel upheld his decision in June.

Bennett, who earlier had said he would take the case to the Supreme Court, said yesterday that a proposed settlement of the case had been presented to the District in July, but that the city had not responded. The settlement would have allowed the police department to proceed with promotions in the detective rank, which have been held up since the suit was filed.