IT CAN'T BE known for years whether South Africa will succeed in its daring attempt to replace the failed authoritarian system of apartheid with a just, multiracial society. But it would be false to the facts and gratuitously dispiriting if every fresh difficulty were taken as an omen of eventual failure. Important steps forward are being made.

A first cycle of progress unfolded from the release of the imprisoned Nelson Mandela. But that first burst of excitement dissipated, and the horizon appeared to be lowering. Fierce white opposition took shape against the changes launched by President F. W. de Klerk. Factional fighting between followers of Mr. Mandela's African National Congress and Zulu leader Mangosuthu Buthelezi's Inkatha took hundreds of lives. The promise created by Mr. de Klerk's and Mr. Mandela's distinctive dialogue seemed to flag.

Mr. de Klerk, however, returning cheered from his warm first reception in Washington, has continued his quest for what he likes to call "the new South Africa." He has now ended the Separate Amenities Act, a legal pillar of apartheid and a law which, though largely overtaken by events in the cities, had continued to regulate life in the rural areas where his National Party -- now officially a multiracial party! -- used to enjoy broad support. Repressive emergency rule was terminated in the holdout province, Natal; there the president acted, he said, confident that with community violence diminishing, the ordinary laws of the land could again take hold. These measures are valuable in themselves and have the bonus benefit of hastening the (early) day when foreign countries can lift the burden that sanctions entail not just for the white minority but, even more, for the black majority.

Surpassing these developments in real difficulty and potential importance is the parallel striving among South Africa's black citizens to compose their own deep differences. The ANC and Inkatha have been moving toward a more respectful relationship that is intended to bring together Mr. Mandela and Mr. Buthelezi for a crucial summit soon. This could contribute to reducing apartheid's ugly legacy of tensions among blacks, and it could produce a common approach to negotiations with the South African government on a new constitution. From these negotiations "the new South Africa" is meant finally to be born.