BLACKS in South Africa have had no single keener grievance than the pass laws, the intricate web of controls by which the ruling white minority restricts their movement within their own country. Some 18 million arrests have taken place under these laws in their 70 years. In 1985, a year of diminished enforcement, 132,000 people were swept up, held to account for travel that would be considered normal and necessary in a democratic country, and jailed or otherwise abused and humiliated. The pass book, which blacks and blacks alone have had to carry at all times, has become apartheid's most notorious badge.

Now the government announces it is abolishing all the pass laws and replacing the hated pass book with a uniform nonracial identity document that will not have to be arried on the person. It is an important breakthrough, and not only for its symbolism. Short of a furtive reinstatement of controls, abolition of these laws will remove one large element of repression from millions of blacks' lives. President P. W. Botha has at last given some evidence -- it alarms the opposition to his right -- of genuine reform. President Reagan, among others who have tried to coax peaceful change, have a display of how it works.

President Botha evidently means not to dismantle apartheid but to lighten its burdens on blacks and thereby to divide blacks and to ease foreign pressures for deeper change. But it is unlikely that even the dramatic act of abolishing the pass laws will slow down the black train.

The work of dismantling apartheid can proceed in two ways. Either the Afrikaners can hold on and South Africa will come increasingly to fulfill a certain image of Northern Ireland, with sickening violence spreading relentlessly. Or Afrikaners can undertake to plan a common future with the leaders of black nationalism, many of whom are in jail. A responsible South African government cannot fail to be measuring the relative risks of the two courses.