The United States needs a national moratorium on the growing practice of reasoning by analogy. Everyone seems to be doing it these days - President Reagan and his critics, news commentators and college professors, armchair philosophers and coffeehouse clairvoyants. It has become a kind of national epidemic, and, like the plague, it is cause for some considerable alarm.
As a graduate student back in the bad old days of the Vietnam war, I recall how the sirens of the Johnson administration would invoke the ''Munich analogy'' as an argument for ''standing up to the communists'' in Southeast Asia. Once before, they darkly reminded antiwar dissidents, the democratic nations appeased totalitarianism. The result, as everyone knows, was the most calamitous war in history.
By the same token, critics of US military aid to El Salvador frequently invoke the ''Vietnam analogy'' in support of their contention that indirect involvement leads inexorably to direct intervention when a legal government is regarded by a large segment of its own population as illegitimate, especially when such a government also happens to be corrupt and incompetent. The Vietnam analogy is being applied to Lebanon as well where some 1,500 to 1,600 soldiers are stationed as part of a 5,000-man multinational force.
But the analogists have really outdone themselves in sizing up the pros and cons of the Grenada invasion. Some see a striking parallel with the Iranian hostage crisis. After all, there were 1,000 Americans on the island, the coup d'etat was carried out in a brutal manner by radical leftists allegedly infatuated with Castro's brand of revolutionary Marxism, and the island, while diminutive, is strategically positioned in an area of vital importance to American interests.
Others see the Falkland Islands crisis as the correct analogy. Grenada is a small, little-known island off the coast of South America; the Falklands were equally obscure patches of real estate in the South Atlantic. The US landed the Marines in Grenada to protect American citizens; Prime Minister Thatcher sent troops to the Falklands to defend British citizens and British honor. Cuba was trying to take over Grenada; Argentina had illegally seized the Falklands.
Still others have drawn very different analogies (and conclusions) in response to the Grenada affair. Richard Barnet of the Institute for Policy Studies compared Ronald Reagan's action in the Eastern Caribbean to Leonid Brezhnev's action in Eastern Europe in 1968. The invasion of Grenada, he suggested, is a lot like the invasion of Czechoslovakia by the USSR. They have their ''Brezhnev doctrine'' (asserting the right to intervene in the internal affairs of the East-bloc countries whenever they deem it necessary) and we have our ''Reagan doctrine.'' Baloney.
In fact, all these analogies are baloney. They all have a fatal flaw: The situations they invite us to compare are not comparable. They mix apples and oranges. The result is a forensic fruit salad, not a firm basis for foreign policy formulation.
The Munich analogy can be invoked every time the US perceives a Soviet presence in any troubled part of the world. Obviously, the promiscuous use (and misuse) of such an emotional metaphor can be as dangerous as the ''threat'' it seeks to expose - Vietnam is a case in point.
Take the Vietnam example. This ''guilt by analogy'' approach has been indiscriminately used by the critics of the Reagan administration to denounce, seriatim, our involvement in (1) Central America; (2) the Middle East; (3) the Caribbean. But, of course, a quick glance at the world map reveals that El Salvador, Lebanon, and Grenada are not located in Southeast Asia nor are they neatly divided into two halves, one popular and effective (our adversary), the other unpopular and ineffective (our ally).
A moment's reflection also reveals that they do not have a large, indigenous population, a national hero-figure like Ho Chi Minh, or a topography that makes the old adage ''war is hell'' sound like an outrageous understatement. In none of the areas where President Reagan has committed US troops have the Soviets made the kind of open-ended commitment they made to Hanoi, in none of these areas do they have a client-state (like Hanoi) that seems destined to dominate the region, and in none of these regions is the outcome of local conflicts so remotely connected to our national interest as it was in Vietnam.
Nothing said so far should be construed as an argument for or against US intervention in places like El Salvador or Lebanon. It is an argument for avoiding the temptation to substitute analogy for analysis. It's time to recognize that analogizing and apologizing are equally inimical to the critical function of press and professordom. The place for Pearl Harbor is in the history books, not on the op-ed pages or the President's prime-time perorations on national television.
At the entrance to the National Archives in Washington, D.C., there is an inscription: ''What is past is prologue. . . .'' If we can put our penchant for analogue in the same place - the past - the quality of the developing foreign-policy dialogue will be immeasurably enhanced.