AT GENEVA, the United Nations has finally brought together for the first time the contenders for power in Namibia, the huge, sparsely populated, mineral-rich former German colony that South Africa has run since World War I. On one side of the table are the local Namibian groups, led by the multiracial DTA, formed under the eye of the South Africans. On the other side is SWAPO, the black liberation organization imperiously blessed by the U.N. General Assembly as the "sole legitimate representative" of the Namibian people. Can the two come to peaceable agreement on independence and democracy for Namibia?

It's a tall order. The white South African government believes the United Nations long ago proved itself to be an unfair bully determined to shove the Soviet-armed, radical-talking, terriorist SWAPO down its throat. SWAPO fears that the South African government is bent on applying its economic and military muscle to perpetuate its own or a client's Namibian rule. It is against those twin presumptions of U.N. partiality and South African chicanery, both of which have surely been in evidence in the past, that the sponsors of the conference are struggling. These last include five Western states in a position to assure and lean on South Africa, an African group in a similar position in respect to SWAPO, and assorted international types. All of them are keen to ease the Namibian afflication and go on to other things.

As will so many other international situations these days, a key figure, President-elect Reagan, is missing.The Geneva conference is unfolding against the troubling possibility that he may step back from the Carter effort to support a U.N. solution and, instead, encourage the residual South African tendency to set up an internal anti-SWAPO group as the independence government. Important Republican figures, dazzled by thoughts of South Africa's strategic potential and Namibia's uranium and diamonds, are advising the president-elect to lean this way. Fortunately, other Reagan administration figures, including (to judge by his caution at his confirmation hearings) Secretary of State-designate Alexander M. Haig Jr., are aware that virtually the United States' whole African position is in the balance. The last thing Mr. Reagan's foreign policy needs for openers is a collapse of the Geneva conference on Namibia.