THE ADMINISTRATION'S decision to exchange diplomats now with Cuba, after a 16-year lapse, is puzzling. For although the exchange of diplomats need not connote approval of either government for the other, this step in its political context conveys unmistakably an aura of improving relations. We had regularly said he is, about Cuban military intervention in Africa: Last year Havana put 20,000 troops, airlifted and supplied by the Soviet Union, into Angola. Yet no sooner does the State Department confirm that Cuba has sent military advisers to Ethiopia than the establishment of "interest sections" in Washington Havana is announced.

Has Fidel Castro been told in effect that he can have the advantages of normalized relations even while continuing unabated the interventionist policy of which the Carter administration officially complains? Is the "real" policy the one spoken by Ambassador Young, who is quoted in Playboy as saying that "a thousand Cubans, or 20,000 Cubans or even 100,000 Cubans anywhere in the world are no threat to the United States"? Has the administration quietly accepted the Castro regime's reported contention that in Cuban dealings with Washington two particular issues are not negotiable - the Cuban military presence in Africa and human rights? Performance on human rights, of course, is the other criterion set by Jimmy Carter for improved Cuban-American ties.

The administration contends that it has lost none of its interest in restraining Cuban activity in Africa. One need not question whether it is losing interest to wonder whether it is losing leverage. The United States has a handful of good reasons, ranging from the strategic to the sentimental, to end its debilitating and anachronistic dispute with Fidel Castro. But it cannot blink away the Soviet-Cuban partnership in Africa. In Ethiopia, moreover, the Cubans cannot claim, as they did in Angola, that they are acting to oppose a move by South Africa. In Ethiopia, they are lending themselves to a Soviet power play, pure and simple, and they are doing it, by the administration's own accounting, by a military move that the United States cannot condone.

The administration is provoking more conservative reaction across the board than its diplomacy may be able to sustain. On Cuba, on Vietnam, on South Korea and on Panama, the Carter administration has stirred the American right. The cumulative impact may be most serious on Panama, since the necessary and long-overdue policy change being pursued there will, if all goes well, produce a new canal treaty that must pass through the Senate. Eventual mutually advantageous normalization with Cuba could be undercut, too, if Jimmy Carter's Cuba policy is not made more consistent and clear.