The Justice Department yesterday asked a federal appeals court to throw out a judicially approved plan under which the city of New Orleans had pledged to promote precisely equal numbers of black and white police officers.

The action was the strongest the Reagan administration has taken against an affirmative-action program. It marked the first time the federal government has formally challenged a court-approved employment quota aimed at relieving job discrimination. The Justice Department attacked the plan for not specifically benefiting those who had been discriminated against.

The administration argued that the New Orleans quota "required innocent non-black police officers to surrender their legitimate promotion expectations to black officers who have no 'rightful place' claim to promotion priority." The Justice Department said the quota violated the equal-protection guarantees in the Constitution.

The action did not come as a surprise. Top administration officials, including Attorney General William French Smith, have said they oppose quotas and favor an approach of "color blind" government policies on discrimination.

New Orleans City Attorney Salvador Anzelmo called Justice's action "incredible" and said it raises "very serious questions" about the department's attitude about civil rights and efforts to end discrimination.

"It is the city's position that the Justice Department has no logical nor legal basis for becoming involved in this case at this time," he said.

The department asked the U.S. Circuit Court of Appeals for permission to intervene in the 10-year-old New Orleans case. It also asked the full appeals court to overrule a decision by a three-judge panel that approved the New Orleans quota last month.

The case dates back to 1973, when 13 black officers charged the city with racial discrimination in its police department. The case was settled before it went to trial, with the city accepting a plan that included an agreement to promote one black officer for each white officer promoted until the police force had a 50-50 racial mix of supervisors.

Female, Hispanic and white policemen immediately opposed the agreement, and a U.S. District Court in New Orleans agreed with the objections, approving all parts of the plan except the promotion quotas. The three-judge appeals panel ruled last month that the District Court should have approved the entire plan.

The eventual outcome of the New Orleans case could affect court-ordered affirmative-action programs in several other major cities.

In Detroit, the courts have ordered the police force to follow a promotion program similar to the New Orleans plan. Similar court orders are in effect for the fire departments in Seattle, St. Louis, Bridgeport, Conn., and other cities. The California state prison system also is operating under a court-ordered hiring and promotion plan.

In seeking to intervene in the New Orleans case, Assistant Attorney General William Bradford Reynolds, head of the Justice Department's Civil Rights Division, argued that the plan would "prefer black officers without regard to whether they had been discriminatorily denied promotions in the past."

Reynolds argued that the 1964 Civil Rights Act "expressly prohibits" court actions that would benefit "persons who were not actual victims of the defendant's unlawful employment practice."

The Justice Department intervention is expected to be one of a number of Reagan administration actions to move into the controversy over so-called "reverse discrimination" growing out of the deluge of affirmative-action cases that followed passage of the landmark 1964 law.