NOTHING IS more worth protesting on the international scene than apartheid in South Africa, and nothing is more painful to those who burn with its injustice and cruelty than the slow and uncertain pace of its change. It is therefore right, reasonable and necessary that a group of black Americans should be trying a new tactic in the struggle against Pretoria's legalized racism. Led by D.C. Del. Walter E. Fauntroy, the group conducted a sit-in at the South African Embassy last week and announced plans to conduct daily demonstrations and other forms of "direct action." The demands made upon South Africa range from the release of recently arrested black unionists to the freeing of black nationalist leaders jailed two decades ago. The "Free South Africa Movement" also calls for an end to the Reagan policy of "constructive engagement."

The American civil rights movement of the 1960s used civil disobedience to draw blacks into open struggle against racial discrimination, and to educate whites on the evils of Jim Crow and enlist them in what turned out to be the successful struggle against it. So now do the sponsors of the new movement set out to make South Africa's injustices more keenly felt and more passionately opposed by Americans, black and white. They hope that American policy will come to reflect more of their own sense of urgency and that in turn apartheid will yield.

Anything that widens the circle of the concerned and brings new attention to the South African pattern of white supremacy has a potential for good. But it is evident that there is sharp disagreement, even among those equally committed to nonviolence, over how outsiders can best contribute to the dismantling of apartheid. The administration speaks for those who would accept the regime as a legitimate regional actor and "constructively" engage with it for foreign policy reasons as well as for purposes of inducing internal change. Critics would take internal change as the overwhelming priority and apply all available pressure to that end. From this position the Free South Africa Movement finds constructive engagement merely a disguise for American support and accommodation of apartheid.

In fact, some tension between the administration and its critics may be a healthy thing. No single strategy of change is going to produce the results within South Africa that will validate that strategy beyond reproof. No administration's policy is going to satisfy the Americans most seized of the monstrous nature of apartheid. Some in the administration are inclined to dismiss black challenges to its South Africa policy as coming from a constituency already indisposed. Those Americans, however, speak for a central feature of the American moral legacy. It is not wrong for them to demand that their government consider their imperatives. South Africans of all races should know that, while there is some division and confusion over tactics, a powerful American majority demands justice.