IT'S EASY TO belittle the gesture made by Transkei, which 18 months ago became the first black tribal homeland to gain formal independence from South Africa, in breaking diplomatic ties with Pretoria. Such is Prime Minister kaiser Mantanzima's reputation as a stooge, and his economic dependence on South Africa, that the idea of a challenge seems bizarre. Only South Africa recognizes Transkei, a place of 3 million people on the Indian Ocean. When it became the first of nine "bantustans" to take independence, virtually the whole world saw only an extension of apartheid: Homeland blacks, rather than being offered equality in Sough Africa, were being dumped into rural slums independent in name alone.

Wa s that too quick a judgment? Chief Mantanzima said at the time that if he had fought for independence rather than negotiated it with Pretoria, the world would have beaten a path to his door. He had a point. He may now, in his fashion, be fighting in a way calculated to win African recognition. His chosen issue is land: He claims a certain area that South Africa is transferring, for administrative reasons, from one province to another. All the homelands want more land; collectively, though they outnumber whites 4 to 1, they possess only a seventh as much. There seen to be various tribal-political and personal factors at work, too, as always. But for the time being, Mr. Mantanzima has severely embarrassed the whites in Pretoria. They cannot easily bring him to heel without advertising that the independence they granted is a sham.

In South Africa two currents are at work, and at cross purposes: ethnic and "national." Whites, playing on real differences, are trying to fragment the population on ethnic or racial lines, the better to maintain white dominance. That is apartheid. Transkei had accepted it, hoping to make it serve its own aims of dignity and development. But tentatively, perhaps still reversibly, Transkei is now trying to get back on the "national" track of reducing ethnic differences and working for a united South Africa whose different groups move toward equality. The uprooted urban blacks, who constitute the whites' work force, mostly support this line, as do the few white liberals.

No country in the world today may harbor greater potential for internal change than South Africa. It is in the process of a messy, massive rolling review of its fundamental character. Transkei, far from being a backwater, is suddenly on the leading wave. Outsiders should watch and try to understand.