THE FOURTH OF JULY weekend is not a bad world has recently turned, in some respects, upside down. It was only in 1975 that the United States extricated itself from a war in Vietnam-in which it had called repeatedly for guerrillas to respect what was taken as an international frontier and to "leave their neighbor alone." When this demand was ignored, the United States attacked the guerrillas' sanctuary-allies' best interests "would be served by the establishment of normal relations" with Vietnam. It is a measure of the shrinking of public interest in post-Vietnam Asia, and of the success of post-Vietnam American policy there, that when the Secretary of State uttered these word in a speech on Asia last Wednesday, virtually everyone yawned. And while obviously one can overdo it, we don't think that's such a bad reaction after all.

By contrast, for some months now the United States has been unfolding its judgment on yet another conflict, in Rhodesia, in which guerrillas are crossing an international frontier. In this one, however, Washington has openly tipped its support not to the target of the guerrillas, what it calls the "illegal racist minority regime" of Ian Smith, but to the country, Mozambique, providing the guerrillas sustenance and sanctuary. When Mr. Smith's troops, not for the first time, struck deep into Mozambique a month ago, the administration criticized him for the reprisal without expressing any objection to the raids that had provoked it. And just the other day at the United Nations, the administration joined a Security Council resolution offering "material assistance" - a phrase meant to preclude armed personnel - for Mozambique's defense. All this is happening, of course, in respect to Africa, a continent which, a few years ago, received about as much attention from most Americans as Asia does today.

Altogether, we beleive, the change is salutary-Africa is in fact a region where the United States ought to be focusing its international attention these days. Its growing strategic, political and economic importance to American interests was underlined by the Secretary of State, in a second speech, on Friday. Moreover, there is a substantial difference between engaging in a costly and protacted land war in opposition to what comes to be widely seen as a national liberation movement in one place, and attempting, by diplomacy and aid, to encourage a movement and political justice in another place.

Still, it does leave one pinching oneself. In a very short space of time, the United States has swung from upholding the status quo in southern Africa; from resisting a guerrilla war across a national border, to sanctioning it and becoming an accessory to it; from contesting a Communist-supported cause, to trying to outflank it. If the shift in American policy makes you a bit dizzy, as it makes us, then it's still well worth nothing on this Fourth of July weekend. For the shift is keeping with the traditional American concern for justice and liberty - values that constitue the special meaning of this holiday.