A FEW CONGRESSMEN, speaking for citizens who feel the United States should go beyond simply deploring Idi Amin's crimes in Uganda, urge that the importing of Ugandan coffee be outlawed. American firms take a third of the crop and, at current prices, pay some $300 million a year for it. By halting American purchases, the argument goes, the United States could weaken a principal economic bulwark of President Amin's power and perhaps bring him down.

But it's not that simple. Most Americans detest the Amin regime. But there has been no declaration of war and, thanks to the tolerance of the other black African states and the support accorded Uganda by different Arab and socialist nations, there is no international consensus for sanctions. Unfortunately, when Mr. Carter said Uganda had "disgusted the whole world," he was wrong.

The limits the truly disgusted countries to steps that, if they are more than symbolic gestures, can hurt the innocent people of Uganda as much as they hurt the corrupt leadership. A coffee boycott seems to us to fall in the latter category. Symbolic gestures are not unworthy; it is just that there should be no illusions about their effects. This is the light in which we view the administration's reported readiness to block the sale of three helicopters and a jetliner to Idi Amin and to train no more Uganda police helicopter personnel beyond the 24 who, inexcusably, are already in Texas. Other countries will fill the gap.

The prominence now accorded human rights in American diplomacy is stirring repeated efforts to make the administration demonstrate its "sincerity" by matching economic deeds to hortatory words. Last week South Africa was the focus; this week it's Uganda; next week, when the Secretary of State visits the country, it will be Argentina; the following week it may well be one or another Arab nation; and so on. Few issues of foreign policy breed more political and ideological contention than the conditions under which the government should intervene in the economic choices made by private citizens and corporations. Our own view is that it is one thing for an American to exercise his right of personal (or corporate) choice and boycott, say, lettuce or grapes - or Ugandan coffee. It is quite another for the American government, dedicated as it generally and rightly is to the politically free exchange of goods in international commerce, to give the impetus of its own fresh example to the boycott principle. The idea of a "coffee break" that would neatly rid Uganda of Idi Amin has a certain instant appeal. But a boycott that would only weigh heavily on already oppressed Ugandans, while setting a dangerous precedent for more of the same political manipulation of international trade in less eregious cases, has no appeal at all. The more we think about where this road might end, the less we think it is one that the U.S. government ought to start down.