With this week's tentative agreement that would bring independence to South African-ruled Namibia in return for an end to the 13-year civil war in Angola, the U.S. just might be on the verge of a diplomatic triumph.

But it's too soon to start celebrating. The agreement in principle leaves some major differences unresolved. Still needed, among other things, are a timetable for the withdrawal of Cuban troops from Angola and a precise agreement by South Africa to implement the United Nations plan for independence for Namibia.Moreover, it would be unrealistic to rule out the possibility that the South Africans may just be buying time to rest their troops and the Angolans may merely be hoping to erode America's military support for anti-communist rebels.

Yet, if the proposed agreement - spearheaded by Assistant U.S. Secretary of State Chester A. Crocker - can be pulled off, it could open the way to improved diplomatic relations between the U.S. and both Cuba and South Africa.

Moreover, the fact remains that just as Russia - which arms Angola and pays Cuban troops - is withdrawing from Afghanistan, it may now wish to cool regional conflicts elsewhere around the world.

In any event, the prospects for resolving the complex conflicts in Angola and Namibia have never looked brighter. Washington should prod not only Havana and Pretoria but also Moscow if the U.S. is to maintain the momentum toward peace in southern Africa.