In Zimbabwe, where I recently visited, there is a certain witch doctor- medicine man (maybe internist, too) who dammed a stream to grow mermaids. He thus restricted the flow of water to nearby farms. The government dispatched an official who reported that the local people didn't think much of the mermaid scheme, but they did of the medicine man. If he were overruled, they thought they would starve to death. At last report, the stream was still dammed.

Chuckle, chuckle, we say -- this is the way things are sometimes in the Third World, where logic and rationality can be scarce commodities and where the crackpot idea of a medicine man can result in the ruination of several farms. But as someone returning from abroad, I find myself thinking the same thoughts about the United States. Logic seems to have taken a powder here.

Take, for instance, the current mild panic over the trade deficit. When I left the country nearly three weeks ago, this was only a potential issue. When I returned, it had achieved such importance that it not only had made the cover of the news magazines, but the president himself was paying attention. As with South Africa, he was trying to figure out a way to stop Congress from taking meaningful action.

You may ask why, after years of massive trade deficits, everyone is suddenly so concerned about the problem. After all, the country has been running a deficit for a decade now -- and the gap has been widening, until this year it will reach an estimated $150 billion. You would think the administration would by now have a plan to deal with it, and in a sense it does. It will continue doing what it has been doing and hope the deficit goes away. This is the American version of growing mermaids.

You do not have to stretch the analogy very far to conclude that Ronald Reagan is our national medicine man. With the exception of some scattered supply-siders who, like theoretical communists, are waiting for their theory to be applied in its purest form, there is almost no one who does not think that the trade deficit is tied to the federal budget deficit. The latter, a $200 billion annual mistake, contributes to the overvalued dollar, which in turn makes American goods noncompetitive abroad.

And yet, the administration and a lobotomized Congress do nothing about the budget deficit. Congress tried in the last session, trimming the budget by about $50 billion, only to learn after recess that it made almost no difference. The fact is that the government is starved for funds. It cannot keep the defense industry rolling in dough and at the same time keep taxes where Reagan put them with his 1981 tax cut. The obvious answer is to raise taxes, but a popular president won't permit it. Like the Zimbabwean medicine man, there is n way around him.

Somewhat the same situation applies in the field of arms control, where only the president thinks that his Strategic Defense Initiative (Star Wars), no matter what its merits may be, can result in the elimination of nuclear weapons. It is this belief, first enunciated 33 months ago, that explains why the president has an almost emotional attachment to his proposal and why he refuses to put it on the bargaining table at Geneva.

In this and other matters, people sort of stand around and wait for the medicine-man-in-chief to change his mind. Former Senate majority leader Howard Baker has now joined much of the civilized world in saying that maybe a tax increase is in order, but nobody, certainly not the president, paid much attention. Instead, the president is pushing for a tax reform bill that would be revenue neutral -- in other words beside the point -- and that oxymoron known as the congressional leadership is wondering whether it can be done.

Keep your eye on Zimbabwe. When they succeed in growing mermaids, we may close the deficit.