AT NYANGA near Cape Town, the white rulers

of South Africa have just written a new chapter in their decades-old drive to dispossess blacks. They invoked a law drawn to deal with immigrant aliens, erected roadblocks and carted 1,500 squatters to one of the rural tribal slums--called "homelands" by the guardians of apartheid. In brief, they expelled blacks from their own country. It was a sickening example of what Ambassador Jeane Kirkpatrick presumably had in mind the other day when she called South Africa "a democracy for whites and a dictatorship for blacks."

A great many Americans feel passionately the wrong of a system that invites outrages like this one. The question is how they should express their feelings about it. It is a question made topical by the arrival of a South African rugby team to play in Chicago, Albany and "somewhere in the Northeast"-- to foil demonstrators the site has not been announced. Some Americans urged the administration to deny visas. Requests have also been made to call off the games on grounds that police will not be able to cope with the violence that the presence of the South Africans may provoke. It is, to us, sad to hear such requests coming from Americans, and especially from black Americans who have special reason to know what it is to be the victims of arbitrary state power. There should be no trace of South Africa's methods in the American protest against them.

But the protests must be strong and real. An enormous peaceful crowd mobilized outside the stadium would have a commensurate impact in Africa and elsewhere. The experience in New Zealand, where the South Africans played before coming here, may show what happens when a demonstration turns violent. Some 7,000 demonstrators did their best to disrupt the last game; scores of people were injured and arrested. Yet the game went on, and it was attended by 49,000 people, a figure suggesting not only that there is a devotion to rugby in New Zealand but also that the effort to prevent the game's being played backfired.

The Soviet Union is said to be ready to demand that the 1984 Summer Olympic Games be removed from Los Angeles if the South Africans play here; there are warnings of an African-Third World boycott. The Olympics-uber-alles crowd at once came out against South African rugby. But it is preposterous to accord the Soviet Union, the world's premier police state, the slightest moral standing to criticize anyone for violation of rights, and it is foolish not to realize that this is only the first of a series of obstacles that Moscow can be expected to throw in the path of the Los Angeles games. As for the Africans, they will have to consider, among other things, whether it matters that the South Africans came here privately, that South Africa is not going to the Olympics anyway and rugby is not an Olympic sport, and that Americans used the occasion of the visit to show they detest apartheid.