ABLE TO LEAP logical abysses with a single bound, American leaders have looked at the crisis in Iran and cheerfully decided that it marks a watershed in American foreign policy, an end to the "post-Vietnam era." America's existential agony after Vietnam is over, congressmen and State Department experts contend, and henceforth the American public will be more willing to accept military intervention in Third World nations without questioning the need. The arrogance of a mob of Iranian students in Tehran, in other words, has unwittingly written out a carte blanche for the arrogance of American power abroad.

The new theory circulating in Washington goes like this: after the disaster in Vietnam, the U.S. grew so timid about flexing its muscles in the Third World that it lost the will and ability to defend "legitimate interests" there. As a result, when the Tehran mob broke traditional standards of international law and took the embassy occupants hostage, America felt powerless to respond. To avoid such embarassing nuisances in the future, the Pentagon's friends in Congress argue, the U.S. must develop a "quick-strike force" able to dump a motorized division anywhere in the Third World within 60 days. Congress approved such a force two years ago, but it took the Iran crisis to convince the White House to finance it.

The new interventionist argument crumbles at the touch of logic. What if that quick-strike force had been at our disposal last month--would it have helped President Carter find a way to get the embassy hostage out alive? Would it have cowed the religious fanatics who provoked the crisis? Would it have accomplished anything except to make America look foolish for having spent billions on it?

The frustration of government officials at their powerlessness in Iran is understandable, but the quick-strike force clearly appeals to their fancy and their vanity, not their common sense. Undoubtedly it stirs fond memories of the Entebbe incident, in which the Israeli government managed to save hostages in Uganda through a clean, neat military operation. But unlike Entabbe, the American embassy in Tehran is not conveniently located at an airport--and the Ayatollah Khomeini does not drive a Mercedes Benz.

AQUICK-STRIKE FORCE would be no help to future presidents faced with crisis like the embassy takeover, except to give them one more option that could endanger hostage' lives. But it would be very convenient for future Secretaries of State who might itch to tip the balance in some civil war in Africa or Asia. Proponents of the force say that today our government understands the dangers of intervening in complex local conflicts, and would only use a quick-strike force to defend our "legitimate interests."

Those interests are open to very different interpretations, however; and a careful examination of the arguments for the force reveals more suspect purposes. Senator Gary Hart (D-Colo.), for example, told The New York Times why we need the quick-strike force: "Our forces aren't structured well to intervene in Third World countries. sixteen infantry divisions don't do you a bit of good in Angola."

But the next Henry Kissinger will have his pet mechanized division to send off to the next Angola, thanks to the recent presidential decision to fund the force. The White House, hawkish congressmen and the Pentagon itself are using the fear excited by the embassy takeover to effect a turnabout in foreign policy too quick for anyone to protest. The quick-strike force makes up only one part of the pro-military campaign; a reinvigorated opposition to ratifying the SALT II arms limitation treaty will undoubtedly follow, and new demands for giving the Central Intelligence Agency more freedom to act covertly abroad will surface after that.

What's worst about this jingoist response is that it obscures the one valuable lesson America might glean from the events in Iran. Air-mobile divisions wouldn't have helped avoid the taking of the hostages; but a more open-minded appraisal of the domestic dynamics of Third World nations, instead, coupled with a more visible reluctance to support repressive dictatorships, surely would. No amount of money spent on flexible military capabilities will protect our "vital interests"--like Middle East oil--as effectively as a wholehearted effort to understand cultural forces like Islam.

Although their actions flout every rule of international conduct accepted in the West, the Iranian students are not unmotivated anarchists but impassioned believers. If we expect to protect our interests from similar fanatics, we must spend some of our billions on educating our leaders and ourselves about them--otherwise, our presidents won't know how to use the brand-new quick-strike force without getting burned. A mechanized division can be surprised as easily as an embassy garrison when its leaders don't understand the opposition.