THERE HAS BEEN another coup in another Third World place where Westerners perceive only dimly what is going on. This time it is in Sudan, a moderate Arab state friendly to the United States. The immediate loser is President Jaafar Nimeri, an army officer who himself seized power 16 years ago in circumstances not unlike those in which his defense minister has taken power, reportedly bloodlessly, now.

Coups come, and those trying to comprehend them reach for a familiar range of explanations. Among the first is always an enumeration of the personal flaws of the deposed leader. President Nimeri was given, especially in his late years, to flights of erraticism -- not least his effort to impose Koranic law on the non- Moslem south. Often there are special misfortunes, natural or man-made, which overwhelm government structures already creaking under burdens of poverty and underdevelopment. Here it may have been four years of drought and a flow of a million refugees from Ethiopia. Then there are the cares added by virtue of a country's links with foreign patrons -- in this case, to keep vital aid flowing from international creditors, Mr. Nimeri had announced price increases that produced strikes and riots and, overall, created a chemistry that made a fresh coup almost a predictable thing.

Nor is it necessarily a bad thing. Mr. Nimeri ruled 16 years. No mechanism existed for an orderly transfer of power. The new man promises to hold power only for "an interim period." Whether he's being modest or simply deceptive remains to be seen. Few would claim, however, that Sudan has only "interim" needs. It is more than a very poor, deeply split country laboring under heavy social and economic disabilities. It is one of many African countries for which the foreign-made models of development and growth seem not to apply.

The United States had played a chancy end game with Mr. Nimeri, putting new chips on him, with a warm Washington reception, just as he was swept off the board. The immediate result is an embarrassment to American diplomacy, but the United States got much value from Mr. Nimeri over the years in strategic and geopolitical coin; he supported the projection of American power in the region and provided important backing for Camp David. Washington now wonders somewhat anxiously whether the new order in Khartoum will see merit in the old order's tie with the United States and the international financial institutions. But perhaps this is the wrong question. Perhaps the right question is what the United States, the International Monetary Fund and the relief and development agencies can do to respond more effectively to the needs of the Sudanese people.