Blacks are surrendering the "moral high ground" of unaided individual accomplishment by pressing for preferential treatment through affirmative action, a black Harvard economist told the National Urban League yesterday.

Glenn C. Loury's speech came after the league had voted earlier this week to reaffirm its longstanding support for affirmative action to help black Americans achieve equality. Loury appeared on the defensive, taking pains to separate himself from conservatives and the Reagan administration. "I'm not here representing anyone but myself," he said.

Loury, who said blacks are exhausting the "good will and tolerance" of the government, stressed that he was simply seeking answers to social problems that continue to face blacks despite past federal programs.

"Blacks continue to seek the respect of their fellow Americans," said Loury, a professor of public policy at Harvard's John F. Kennedy School of Government. "And yet it becomes increasingly clear that, to win the equal regard of their fellows, black Americans cannot substitute judicial and legislative decree for what is to be won through the outstanding achievements of individual black persons . . . .

"For what ultimately is being sought is the freely conveyed respect of one's peers," he added. "Assigning prestigious positions so as to secure a proper racial balance . . . seems fundamentally inconsistent with the attainment of this goal . . . .

"This is especially so with respect to the policy of racially preferential treatment, because its use to 'equalize' can actually destroy the good which is being sought on behalf of those initially unequal," Loury said.

He spoke after Bernard E. Anderson of Princeton University's Woodrow Wilson School of Public and International Affairs contended that "black conservatives" are wrongly interpreting conservative principles.

"During the past few years a group of black conservatives has emerged as prominent critics of social policies designed to help the disadvantaged," he said. "But this new ideology is a curious application of conservative principles. Conservative principles advise prudence and caution . . . but the new conventional wisdom leads in the opposite direction.

"It is legitimate to ask what is conserved when there are thousands of minorities looking for work and unable to find it? What is conserved when the hopes, the dreams and aspiration of the future of young people are cruelly dashed upon the the rocks of unemployment . . . . "

Anderson further argued that to halt the use of affirmative action in the name of glorifying individual accomplishment is to ignore "the experience of history and present reality."

He said quotas have been used properly by the courts in cases where judges have found "denial of basic rights."

"Affirmative action in all other instances," he said, "means no more and no less than taking special pains to remove all vestiges of discrimination by making sure qualified minorities and women are included in the relevant applicant pool and are seriously considered for available positions . . . .

But Loury said despite past opportunities designed to help blacks, they still lag behind whites.

He cited the academic world, where, he said, blacks still score an average of more than 100 points below whites on the Scholastic Aptitude Test and the percentage of black college students is declining.

Loury said black students need to better prepare themselves: "Is there so little faith in the aptitude of the minority young people that the highest standards should not be held out for them?"