ORDINARILY, the United States would not be paying much attention to what was going on in Chad, an impoverished land-bound former French colony in West Africa. The latest turn, however, cannot easily be ignored. A long desultery civil war seems to have ended in a victory of Libyan -- that is to say, Soviet -- arms. The avenging Col. Qaddafi, Moscow's North African favorite, sent tanks across the border and across a thousand miles of desert, and the battle was won.

To be sure, he was invited in by Chad's president. That makes formal protest difficult. But it does not change the central political fact. A radical interventionist Soviet-sponsored regime has successfully used force to alter the balance in a sensitive part of formerly French Africa. That the defeated side was widely reported to be supported by Libya's Arab arch rivals (and the United States' friends), Egypt and Sudan, sweetens the victory for Col. Qaddafi. Few would maintain Chad is the only place in the region where he wishes to be the arbiter of power. Certainly it is far from the only place with the tribal, religious and other rivalries tht provide the fodder for intervention.

Until as recently as last spring, French troops stationed in chad might have held the situation in check. Upon request, however, France withdrew its remaining forces. This was supposed to set the stage for a local settlement. But instead, the president called in Col. Qaddafi, who has dabbled in and harassed Chad for years -- he has occupied a border strip said to contain uranium ore and iron. Unfortunately, the French could not organize themselves to send forces back in.

If there is one positive result of the Libyan expedition, it is the contribution it has made to the political education of Chad's other neighbors, and of West Africa generally. Both the weak formerly French states like Central African Republic and Niger and a strong formerly British state like Nigeria may now finally be coming to grips with the fact that Chad gives Libya what has been called a bridgehead across the Sahara from Moslem North Africa into black Africa proper. One should not use such strategic metaphors glibly; the reality is duller and more complex. But surely Africans have a greater interest than anyone else in determining whether they wish to stand by while an outlaw regime like Col. Qaddafi's, which has eagerly lent its Islamic impulses to Soviet Communist strategic designs, redraws the map of their continent.