THE COURAGEOUS and irrepressible Bishop Desmond Tutu, back now in South Africa, has made his first use on home ground of the stature and protection accorded by his new Nobel Peace Prize. Addressing the foreign companies that do business in his country, Bishop Tutu demanded that they actively work for far-reaching social change. If there is not fair progress in two years, he stated -- and here he was bumping against a law that criminalizes advocacy of sanctions -- "the pressure (on South Africa) must become punitive and economic sanctions should be applied."

The particulars remain to be elaborated. The heart of the Tutu appeal, however, makes good sense. Foreign corporations are a small but influential sector. Under the Sullivan principles, written by the Rev. Leon Sullivan of Philadelphia, an effort has been made by some of the American firms among them to become what Americans would call equal opportunity employers. Building on this base, Bishop Tutu seeks to enlist all foreign companies and to induce them to tackle larger issues: abolition of the migrant labor system, housing black workers with their families, ending the pass laws, broadening union rights, advancing black education.

Will it work? The Sullivan principles have helped, though they have had too little steam behind them. A more sustained approach is needed. American firms, which operate in another political environment at home, may turn out to be more responsive than European and Japanese firms, but all should be held accountable. For the two premises of the Tutu proposal are unassailable. One is that companies profiting from the cheap black labor that apartheid makes available have a moral obligation to combat the iniquity of the system. The second is that the companies are in fact operating in a society open to change by their exertions -- not wide open, not easily open but open to purposeful, persistent reform all the same.

Therein, of course, lies the fragility of Bishop Tutu's position. Many whites regard him, falsely, as a carrier of revolution. Many blacks see him as one who does not understand that the time for reform is past. The bishop hopes against hope they are wrong. But, evidently to accommodate their impatience, he declares that if his reformist approach does not bear early fruit, "the pressure must become punitive."

Just what the effect of sanctions would be on white privilege is much debated. There can be no question, however, that the immediate punishment would fall greatly on blacks, who depend on the white-run South African economy for their livelihood and for what opportunity is open to them. It is precisely to forestall the possibility of such a deepening tragedy that Bishop Tutu calls on the foreign companies to play a larger role.