USUALLY WHEN a foreign government sharply reduces the American presence and kicks out most American officials, it's cause for a certain dismay. But in the case of Ethiopia, which announced such actions over the weekend, it may be something of a blessing. The reason is that the military government now seated in Addis Ababa is in deep trouble and, since there does not seem to be much the United States can or perhaps ought to do to help out, it might as well keep its head down. American diplomacy was headed in that direction anyway. The Ethiopians have accelerated the pace.

It was not always so. Through the cold-war decades, Washington supported Emperor Haile Selassie, who in turn offered himself as an African political partner and provided rights to a major communications base in Asmara. But three years ago the emperor's domestic misrule caught up with him, and he was overthrown. It was chiefly his successors' need for American arms that kept them tied to Washington. Almost inevitably, once they made other military connections - with Russia for equipment with Cuba for advisers - they started breaking the American connection. The Carter administration's public attack on their human-right record seems to have been the last straw.

Does it matter much? For supporting Addis Ababa, which faces a serious secessuonist challenge from its Red Sea privince of Eritrea, the Soviet and Cubans will win respect from some Africans, suspicion from others. Neighboring Somalia, until now a Soviet client, Is being ardently wooed back into the and Marxist camp by Saudi Arabia, among others. Moscow presumably hopes for access to the port Djibouti in the "Territory of the Afars and Issas." tucked up between Ethiopia and Somalia on the Gulf of Aden, on which France is about to confer independence. But the chronic turmoil and instability in the region make any foreign power's "strategic" gains there of dubios value and permanence. There is no reason and, given due American discretion, much likehood of a great-power confrontation, even through proxies.

The United States has a large and necessary interest in the Arab-Israeli conflict and the southern African, as in Ziare and the other corners of the continent where neither of these questions intrudes, the United States would do well to step back from high visibility or direct involvement. Various other foreigners will come in: the Russians in Ethiopia, the Saudis in Somalia, the French and Moroccans in Zaire, and so on. It would be infinitely preferable if Africans were more prepared to solve their own political problems. But their weakness and their divisions, they will seek or receive outside patronage. The United States should do what it can diplomatically to localize, and ease, these conflicts. But the thrust of its policy should be to help those Africans ready to be helped to tend to their immense economic and social cares.