FEW AMERICANS have earned a more attentive hearing on South Africa than the Rev. Leon Sullivan, the Philadelphia minister who wrote, promoted and policed the ''Sullivan Principles.'' His equal-rights code for corporate conduct under apartheid has been, in the consensus judgment, a major success in changing the policies of American companies and in inducing South African companies to pick up the same policies. So it is important to understand why he has now decided to abandon the effort and to try to force the remaining 200 (of 300) American firms, including the most conscientious Sullivan practitioners, to quit South Africa.

Mr. Sullivan believes that the Principles, along with other measures, failed to ''work'' -- to force the regime to dismantle apartheid promptly. He is, of course, right. Neither earlier nor in the last year or two of intense Western concern have the Principles, based on targeted engagement, or sanctions, based on punitive disengagement, ended apartheid. They have altered some specific practices, but they have not brought down the system. They may even have reinforced official determination to resist foreign pressure and advice to hold on.

Mr. Sullivan is aware of this, but, despairing of short-term political progress and resigned to the immediate losses to blacks who have profited from the code, he now accepts the view that the accumulation of pressure is the only way to go.

In a society so conflicted as South Africa, no one can say with certainty what particular approach will work. It seems to us anomalous, however, for the author of a program that has benefited tens of thousands of blacks and held out hope to many more should deny his own child on the basis that it did not accomplish the maximum goal in a short period of time.

The economy is an instrument of white control, but it is also an instrument of black progress. The Sullivan Principles have insulated the foreign firms applying them from divestment pressures, but the Principles have also launched, in Mr. Sullivan's earlier words, ''a revolution in industrial race relations across South Africa.'' He has represented a kind of center in the American debate on apartheid, a center that is not holding very well. But his code remains too valuable to South Africa's blacks to abandon summarily. The firms now thinking of continuing ''the Sullivan Principles without Sullivan'' seem to us to be on the right track.