Civil rights leaders rallied round the banner of affirmative action yesterday on two fronts, as the U.S. Civil Rights Commission issued a detailed endorsement of affirmative action that coincided with a dust-up on the issue in the Senate.

Contrary to what critics of affirmative action claim, white men continue to benefit from "an interlocking self-perpetuating process that, started by past events, now routinely bestows privileges" on them, according to the commission report. It works against blacks, women and others to an extent that renders many "color-blind" or "neutral" actions discriminatory, the report says.

It reasserts that affirmative action, including quotas in certain cases, is the only remedy.

Outgoing commission chairman Arthur S. Flemming, who was fired last month by President Reagan, presented the 56-page report with a denunciation of attempts by Congress and the current administration to "pull the rug out from under" efforts to gain equal opportunity for blacks, women and others.

The administration, among other things, has indicated that it will no longer ask courts to force employers to meet numerical goals for hiring women or minority group members, but will seek action in individual cases of proven discrimination.

Also, in an interview yesterday in The Wall Street Journal, Assistant Attorney General William Bradford Reynolds said he will seek a Supreme Court ruling to bar federal agencies from developing plans that would give minorities and women preference in hiring and promotions.

On Capitol Hill yesterday, Sen. Orrin G. Hatch (R-Utah), an avowed foe of affirmative action, heard civil rights supporters make their case at the latest hearing by his Labor and Human Resources Committee.

Veteran civil rights lawyer Joseph Rauh Jr. called the gap in earnings between white men and other groups "a national scandal." He pointed out that unemployment for blacks and other minorities stood at 15.5 percent last month, more than double the rate for whites.

In a day of conflicting testimony, economist Walter E. Williams of George Washington University countered that the affirmative-action approach "offends every single principle of individual liberty, individual accountability and fair play."

"President Reagan utilized the principle of affirmative action," Rauh retorted, by appointing Sandra D. O'Connor to the Supreme Court and Samuel R. Pierce Jr., a black, as secretary of the Housing and Urban Development Department. The two were qualified but were not the most expert in their fields, he said.

When Sen. Edward M. Kennedy (D-Mass.) noted that the president was carrying out a campaign commitment, Hatch remarked that, "After the last four years, it's nice to see the president who lives up to his commitments." "Like a balanced budget," Kennedy shot back.

Flemming said that, contrary to belief, affirmative action does not require employers to hire unqualified people. "Firing whites or men to hire minorities or women, and choosing unqualified people simply to increase participation by minorities and women, are universally condemned practices," the report says.

The report, called "Affirmative Action in the 1980s: Dismantling the Process of Discrimination," endorses the use of quotas in certain situations -- "when they are needed to dismantle discriminatory processes" -- but opposes "the use of quotas that derive from prejudice . . . ."