THE U.N. GENERAL ASSEMBLY last month whooped through a resolution calling for a worldwide radio campaign against one of its members, South Africa. The Secretary General, Kurt Waldheim, would prepare programs, and members with transmitters would broadcast them. But its turning out to be difficult to enlist members with suitable shortwave broadcasting facilities to do the transmitting. The Russians and Chinese have no objection to propaganda but it has to be their own; they may also be skittish about sanctioning a precedent of beaming official international broadcasts to a country that doesn't approve them. Notwithstanding appeals by the British Foreign Office, the British Broadcasting Corporation does not want to undermine its greatest asset - its credibility - by going openly into the propaganda business. The West German and the Dutch radios seem to have similar reservations.

At first, on the basis of a misunderstanding, the United Nations assumed it would have full use of the Voice of America's transmitters in Liberia. The Voice already routinely "feeds" U.N. straight-news reports to African governments requesting them. But the Voice has since made clear that it must have complete control over its direct broadcasts: It won't hand over the mike. Moreover, the Voice says, its current transmitters in Liberia cannot reach South Africa reliably anyway; for that very reson, it is even now-belatedly, we might add-building more powerful facilities with which for the first time to blanket sountern Africa.

We're pleased to hear that the integrity of the Voice is being protected. Apartheid deserves condemnation, as does much else, but that is not reason in itself for the Voice of America to yield up its basic function of being the voice of America. When officials of the United States, or citizens, express their various and complex views on South Africa, then the proper business of the Voice is to communicate them. To broadcast programs prepared by the U.N. Secretariat at the direction of the General Assembly is something else. We mean no disrespect to the Secretary Genera l when we say that the Voice of America cannot be the Voice of Kurt Waldheim.