(FORTUNE Magazine) – Everybody agrees that the United States has won a great diplomatic victory in southern Africa. Well, everybody who matters. Among those enthusing about the victory as we went to press (just before the election): the U.S. State Department, editorial writers at the New York Times and Washington Post, and position-paperists for Candidate George -- who cited this sterling diplomacy in his first debate with Candidate Mike (whose own position was less clear). Among the negativists we counted only a few hard-line characters like Senator Jesse Helms of North Carolina and, er, the present writer. Although not yet set in concrete, a deal in southern Africa is visibly taking shape. It has been worked out by representatives of Angola, Cuba, and South Africa, with the U.S. functioning basically as a mediator rather than a principal. Nevertheless, the package that is emerging is one that the U.S. has been trying to put together for eight years. Its principal architect has been assistant secretary of state Chester A. Crocker, a fellow whose acumen we have brooded about ever since the congressional testimony in which he referred to the Communist-dominated African National Congress as ''freedom fighters.'' As usually outlined, the deal will have these elements: The Cubans, who now have maybe 50,000 troops in Angola, will pull them out. The South Africans, who have already withdrawn all their own forces from that country, will also leave Namibia. Then, under United Nations auspices, Namibia will elect its own independent government. This is stated by Crocker to be a great deal for his side. You could argue, however, that the deal advances Soviet interests far more than our own. For one thing, Namibia under independence figures to be another Soviet client state: Everybody agrees that the Southwest Africa Peoples Organization (Swapo) will control the country after the election, and most agree that Swapo is basically a Communist operation. State Department folks tend not to talk a whole lot about Swapo in assessing the deal. | And, unfortunately, there is no reason to suppose that this loss in Namibia will be offset by a gain in Angola. The main reason the U.S. wanted Cuban troops out of that country was that, in their absence, the Marxist-Leninist government there would be dangling from lampposts in 20 minutes and there would be one less Soviet client state in Africa. In the wake of the deal, however, it appears that the Angolan government can survive unhung. Its main opposition, the Unita forces led by our ally Jonas Savimbi, is instantly much weaker with the South Africans gone. Furthermore, it is not clear when the Cubans will leave Angola -- or, indeed, if all of them ever will leave. Here we come to the strangest aspect of the deal. Its two main elements, after all, were reciprocal withdrawals by the Cubans and South Africans. All logic says they should have left at the same time. In fact, it now appears that the South African withdrawal from Namibia will have been completed by mid-1989, while the negotiators are still arguing about whether the Cubans pull out over two, three, or four years; furthermore, some on our side (e.g., Savimbi) have begun to sound as though they are reconciled to a permanent Cuban presence at some level. Okay, why will there not be simultaneous pullouts? Answer (supplied by a State Department official): ''The logical deal is not achievable.'' In other words, the Cubans said no dice, and had the muscle to make it stick. Their muscle materialized in mid-1988, with a rapid, major Cuban-Soviet buildup in Angola. Everyone agrees that the Cuban forces there suddenly increased by something like 25%, and that the buildup enabled them, together with a force of Soviet advisers, to clobber the South Africans in decisive fighting last summer. It was this defeat, which led the South Africans to throw in the towel, that made Crocker's deal possible. Because South Africa is a pariah state with reprehensible racial policies, nobody in this country wants to admit that it has been an important military ally of the U.S. But it surely has been, and its defeat by Soviet-bloc forces is also a defeat for the West. Even if the Washington Post views the outcome as ''one of the stunning achievements of the Reagan years.''