IF THE REAGAN administration has any hope at all of improving its relationship with blacks, something is going to have to be done about the prose of Clarence Pendleton Jr., chairman of the U.S. Commission on Civil Rights. If the commission as an institution wants to maintain any credibility as an independent body exploring and seeking to remedy problems of racial conflict, individual commissioners are going to have to speak quietly to the chairman or speak out loudly to counter some of his assaults.

Policy differences are to be expected. Mr. Pendleton has always made clear his disagreement with most civil rights leaders on the question of affirmative action. Like others in the administration, he rejects the use of numerical goals and quotas in fashioning remedies for discrimination, and he opposes the concept of comparable worth. There are perfectly legitimate reasons for supporting these positions, as there are for opposing them, and people of good will do disagree. But instead of conducting a rational and respectful debate, the chairman makes broad, unsupported pronouncements and attacks the motives of those who disagree with him.

Mr. Pendleton may wish, and the Justice Department may argue, that because of a Supreme Court decision last year in a case involving Memphis firefighters, racially based numerical remedies "are a dead issue." But that is far from a settled matter. The Memphis case involved a seniority system, layoffs and an employer not found to be intentionally discriminating. Lower federal courts have continued to uphold remedies encompassing numerical goals in cases where the facts were slightly different. The Supreme Court has yet to pass on these decisions.

It is true that Mr. Pendleton himself has been treated pretty roughly by his critics. But he goes a step further in attacking the motives and integrity of civil rights leaders who do not share his views on this issue. Recently, he has called them "racists," "immoral" and "part of a race industry and . . . a problem for black progress." No one else in the administration, black or white, speaks in these terms, and such inflammatory language is uncalled for. So was a comment that comparative worth is "the looniest idea since Looney Tunes." The chairman's style has become troubling even, it seems, to those who may agree with him on substance. He can't be doing his cause much good.