SOUTH AFRICA declared a formal state of emergency in order to head off observances of the 10th anniversary, tomorrow, of a famous protest in which police shot down unarmed blacks protesting apartheid peaceably in Soweto, white Johannesburg's huge black satellite. But South Africa already was in a state of permanent social and political emergency, a condition to which the white government's continuing embrace of apartheid consigns the whole country, involuntarily and fatefully. The extra police powers the government assumed to allow it to deal summarily with the emergency of its own creation take it that much further away from dealing with it wisely and effectively -- by political consultation and accommodation.

In the last few years an unstable new chemistry has come to South Africa, compounded of white efforts to save privilege by modernizing or reforming apartheid and black efforts, freshened by the spectacle of white review, to ensure liberation and equality. But the concessions undertaken so far have only fractured the white minority without accommodating the black majority. The government of P. W. Botha has made feints but not substantial moves toward setting up a political process that would give moderate blacks a fair chance to demonstrate that armed struggle is not the only path to the future. President Botha's declaration of emergency, even while he receives Bishop Tutu for the first time in six years, is in this pattern of clenching the fist of one hand and beckoning inadequately with the other.

Continually, others beyond South Africa have sought to break the cycle. The latest to try are an ''eminent persons group'' from the British Commonwealth. It started out opening up lines to the Botha government and to key elements of the black leadership, including the imprisoned Nelson Mandela, and positioning itself to make a continuing contribution to what must necessarily be an uncertain dialogue. Then, strangely, it quit on grounds that the government had rejected its first set of proposals. Sanctions, the group now tells a reluctant British government, are the only answer. In its own political context, the American government is coming under similar demands.

Whether fuller sanctions would bring more gain by shocking the whites into political compromise than they would cost in economic distress to blacks and in diminished foreign access to Pretoria is a fair question, but it is one not much debated anymore, and partly for good reason. Events have shown that South African blacks are not going to wait upon the debates of others to demand their freedom. As black actions have increased as an engine of change in South Africa, sanctions have diminished in importance. That reduces the principal argument now heard for them to the making of a moral or political statement.

Statements are vital. The first place to make them, however, is in words. Here it must regrettably be said that President Reagan has been speaking with a thick tongue, criticizing emergency rule but in terms that undercut his criticism. He has, for instance, equated the violence of the enforcers and the victims of apartheid. On him falls a great responsibility to ensure that South Africa takes no false comfort from what he says.