I have generally felt glad whenever a black person obtained any significant position in society -- whether it was mayor, cabinet member, Supreme Court judge or newspaper editor. But in the case of the news reports that the Reagan White House intends to nominate North Carolina businessman Robert Brown as the next ambassador to South Africa, I feel a sense of skepticism tinged with ambivalence.

In view of the administration's stony resistance to change in South Africa, the appointment not only smacks of tokenism, but also is suspect. Some Reagan administration officials have already acknowledged that Brown's nomination is partly an effort to buy time. As the Senate stands poised to vote for tough economic sanctions against South Africa, the administration, whose policy of constructive engagement has flopped, has hit upon the idea of making Brown the U.S. ambassador. Brown's nomination would, in their reasoning, symbolize American commitments to the black people of South Africa and encourage black-white negotiation.

But the problem with the administration's ploy to buy time is that time has just about run out in South Africa. More than 1,700 people have been killed and thousands have been arrested in the past two years. We have passed the point where naming Brown can stop the bloodshed or give South Africa time to chart a new course in race relations. Many U.S. senators are well aware of just how high South African strife has risen. "We are at the very end of the possibilities for achieving peaceful change," said Sen. Lowell P. Weicker (R-Conn.) The senator might have added that the U.S. reputation as a defender of liberty and freedom for all people is at stake as well.

Although our nation's reputation has already been badly tarnished around the world by its policies in South Africa, using a new messenger, in the case of Brown, to carry a failed message, will not restore it. Yet there is broad agreement that a black ambassador would bring special symbolism with him to that unhappy land.

Indeed, the idea of sending a black ambassador to South Africa seems to have surfaced in an article by Sanford J. Ungar and Peter Vale in the Winter 1985/86 issue of Foreign Affairs Magazine. Examining why constructive engagement had failed and putting forth a dozen policy initiatives that the United States should undertake, Ungar and Vale suggested as one of them a black envoy who would "demonstrate important points of principle to South Africans of all racial groups (and above all) would be an opportunity to emphasize the valuable role that black people play in a multiracial society and a system which South Africans often compare to their own."

The new envoy could avoid being a token, these writers suggested, by making "it clear that he is the ambassador of all Americans to all South Africans, not just of white America to white South Africa."

In addition, according to Eliot P. Skinner, Franz Boas professor of anthropology at Columbia University and a foremost authority on Africa, "the symbolic fact is crucial since South Africans have used race . . . as its raison d'etre. Now they must recognize that the U.S.A. has understood that use of race is a hostile act in the present global system. So this could be a very good appointment in terms of its symbolic value in the contemporary world."

And what of the man who, if nominated and given clearance, is expected to negotiate in these shark-infested waters? Brown, a former special assistant to President Nixon, has no diplomatic experience. But several former ambassadors do not see Brown's lack of diplomatic expertise as a barrier if he has management skills and President Reagan's confidence. Brown's former associates from his White House days say he used power effectively while giving blacks needed access to the president. "The duty of a person taking this kind of appointment is to make sure you accomplish the president's objectives while striking a blow for the brothers and sisters," said Arthur Fletcher, former assistant secretary of labor when Brown was in the White House. "From what I know of Bob, I think he can do it."

But the real test for Bob Brown, if he is appointed, will be whether he can carry out the Reagan administration policies and help the South African government move toward the total enfranchisement of its 24 million black citizens, while avoiding becoming another black sacrificial lamb on the altar of apartheid.