PIET KOORNHOF, point man of the South African government's effort to forestall black revolution by white reform, has been in Washington lobbying. He has essentially two arguments. The first is that South Africa's problem is not one of advancing human and political rights as the West commonly defines them, but of respecting the real and natural differences among the country's "cultures" or races in ways ensuring dignity and progress all around. The second argument is that South Africa's white establishment is irrevocably committed to reform and is moving toward a "brilliant" future, and that it would do even better if it were no longer branded as "the polecat of the world."

No mere liberals' pet, Mr. Koornhof is a steadily rising figure in the party that dominates his country's political life, and the minister chiefly responsible for substantive racial questions in a government uniquely "enlightened," as South Africans say. The reforms he has presided over and helped plan make South Africa perhaps the most lively and ambitious social laboratory in the world today. Even among South African blacks schooled to the deepest suspicion of their white rulers, some people are now tentatively testing the new claims of white sincerity and asking if it may not be possible to avert what a former prime minister described as a prospect "too ghastly to contemplate."

This evidence of hesitant interest among some South African blacks in what makes it necessary to take South Africa's "deep reform" seriously. Most Americans, applying their own standards to this program, would probably pronounce it a pale effort to buy off a black "silent majority" with skimpy material concessions and second-class political rights. The enthusiasm of the country's whites for what they hope will be a workable escape hatch is, finally, of only marginal interest. But if nonwhites come to see in reform an alternative to continuing humiliation and eventual revolt, that is something real.

It will take a year of two or three to see the full dimensions of the black response. During that time it makes little sense for countries like the United States to prejudge the black decision by, for instance, restricting American investment in South Africa. This is the current litmus South African issue in American political debate. With a cynical government in Pretoria, foreign investment strengthens apartheid. With a sincere government, it promotes the economic growth that can help South Africa escape apartheid. Such a determination is too important to remove from black South African hands.