AN EXTRAORDINARY formal 18-month effort to change the rules by which the wealth of the world is distributed has come to an inconclusive end in Paris. Given the immensity of the task and the differences among the players, no other result from the Conference on International Economic Cooperation, often known as the North-South dialogue, was conceivable. The (non-Communist) industrialized nations could not have been expected to do more than prudently trim sail to the stronger but still uncertain winds - actually, two winds - of the poor undeveloped countries on the one hand and the oil-rich but also undeveloped countries on the other.

The Carter administration's rhetoric of sympathy for the Third World may have led some listeners to anticipate a more generous policy. But domestic economic and political necessities are all too constant. The point is underlined by the difficulty the administration will have in making good on its highly conditional Paris pledge of an extra $375 million in aid. It can only reduce misunderstanding if that point is understood all around - as it seemed to be at Paris.

The North-South dialogue represented essentially an effort to cope with the three-year-old price revolution. The poor countries at least drew attention to their demands for debt relief, enhancement of their earning and buying power, and more aid. The oil producers steadfastly resisted the oil importers' attempt to set up a permanent forum in which the consumers could have a continuing say on oil price and production levels. The industrialized states strove to diffuse the Third World's attack on their privileges by dispersing discussion of particular issues to quieter forums in whichthe rich have more control.

The traditional American faith in economic expansion, as something providing new gains to others without forcing new losses upon the United States, has undergone heavy erosion in recent years. But Americans, though they pride themselves on their sympathy for the less advantaged, are still far from ready to yield income or purchasing power or jobs to citizens of other lands. For an administration as determined as Mr. Carter's to play a broad international role, this poses a difficult problem, no less critical in the long term for not being acute in the short term. The President cannot fully satisfy either domestic constituencies or foreign partners.But neither can he stop trying to do as best he can.