MR. REAGAN GOT IT wrong in his South Africa speech yesterday. Something new was needed: something to make it clear not only that he feels the great wrong of apartheid but also that he is not letting pride stand in the way of an evolution of policy. Yet for all the strong words he mustered about apartheid, he still does not convey anything like the urgency its victims feel for getting out from under it. He still apparently believes there is time, political space and company to go on with business as usual. This attitude threatens to leave him marooned behind onrushing events in South Africa and here at home.

There is a disconcerting rigidity to Mr. Reagan's thinking. Somehow he has got the sanctions question framed in artificial either/or terms. ''We must stay and work,'' he said, ''not cut and run.'' In fact, if Mr. Reagan were going to fulfill the promise of stay and work, he would have committed the United States to an expanding dialogue with the African National Congress, one of the key groups with which the Pretoria government must negotiate on a basis of full equality. In any event, it pins a false rap on sanctions to identify them with cut and run. Unenforceable, indiscriminate sanctions of the sort the House adopted in a fit of theatrics and distraction may deserve that label, but sanctions like those recommended by the recent British Commonwealth mission belong to a sensible stay-and-work policy. The Commonwealth would cut at the travel, financial options and psychological ease of whites but exclude controls on the metals of strategic value to the West. It anticipates not the destruction of South Africa's economy but its temporary, though considerable, dislocation.

The Reagan speech unhappily aggravates and advertises divisions in Washington. The silver lining is that it may have the practical effect of drawing the Republican-controlled Senate into a larger role. Moderates such as Richard Lugar and Nancy Kassebaum favor an effort to keep up with fast-moving political currents and to steer them by application of particular sanctions in stages. This is the approach the president might have taken in order to retain control of American policy. He stands increasingly to lose control now.