IN A BURST OF anticolonial innocence a decade ago, the United Nations designated the South West Africa People's Organization as "sole" representative of the people of South West Africa, the South African colony known to the international community as Namibia. Just why the United Nations anointed SWAPO, then as now just one of a number of nationalist organizations competing for power, we don't happen to know. We do know, however, that the U.N.'s choice seems to be the chief obstacle standing between Namibians and a freely chosen government of their own.

SWAPO, whose power base is in the Ovambo tribe in northern Namibia, runs guerrilla operations out of southern Angola. It wants the credit for expelling South Africa, which took over Namibia under a League of Nations mandate in 1920. Mostly, it wants power. SWAPO has demonstrated this by persuading Tanzania and Zambia to imprison hundreds of its dissidents and by resisting the idea of free elections - evidently it fears to lose. Five Western nations ("the five") have been trying to negotiate the transfer of power to an elected government. But - here is the sticking point - Pretoria will not withdraw its troops or let them be "neutralized" by a U.N. presence, so that fair elections can be conducted, unless SWAPO makes similar concessions, and SWAPO isn't bending.

It is widely accepted that South Africa has no right to be in Namibia at all. But the fact is that Pretoria is finally preparing the territory for self-determination. Apartheid is being demolished. Multiracial political organizations are rising. SWAPO's friends insist that South Arica is trying to steer Namibia, which it both milks and maintains, toward an economic and political system congenial to its own interests. But what state does not want friendly and stable neighbors? The crucial test should be whether, if "the five" fail to draw in the externally based SWAPO, South Africa will arrange a free and fair "internal" transition to independence. The answer should be known soon.

The problem is the United Nations. The South Africans are offering externally based SWAPO forces the opportunity to participate peaceably in th political process. The United Nations should 1) encourage SWAPO to test that offer, 2) provide a presence during elections to ensure that SWAPO gets a fair shake and 3) pledge to respect the outcome of free elections no matter how they come out. Or does the United Nations intend to sponsor an armed attack on a government more freely chosen and representative than that of perhaps nine-tenths of its own members?