Iran and the Persian Gulf have been nightmares for American policy makers since the fall of the shah. Confusion over how to define and defend vital interests brought down President Carter and has blighted President Reagan's second term. The latest chapter has seen U.S. policy lurch from clandestine arms and intelligence support for Iran in its land war with Iraq to a decision to side with Iraq in its naval war with Iran by escorting Kuwaiti ships thinly disguised as American vessels.

Any assessment of what is by its nature an open-ended commitment in the Persian Gulf must begin with a discussion of America's vital interests there.

Freedom of Navigation: During the 1970s the interruption of Middle East oil supplies ushered in a decade of inflation, unemployment and severe recession. Another oil crisis -- and closure of the Gulf would produce such a crisis because half of the world's oil reserves are located there -- would have consequences at least as severe.

To be sure, Europe and Japan have an even greater stake in freedom of Gulf transit than the United States because much more of their oil comes from the Gulf. Under any rational allocation of responsibilities they should carry a major burden in protecting the oil supplies.

Unfortunately the allocation of burdens is not always rational. In the end America is trapped by the reality of its own interests, even if its allies fail to see theirs. Oil is fungible; if Persian Gulf oil is interrupted, Europe and Japan will bid up prices at other sources of supply, thereby regenerating the inflationary spiral of a decade ago. The United States may be obliged to defend access to the Persian Gulf alone. America's allies should have no illusions, however. If the United States is forced to act unilaterally, already strong congressional and public disenchantment with the allies will be magnified. Still, The United States cannot ask for a blank check; it has the obligation to define carefully in consultation with its allies the threshold at which freedom of navigation is in fact at stake.

The Iran/Iraq War: The fundamental reality of the Iran/Iraq war is that it is against the interests of the industrial democracies (and perhaps of the Soviet Union) for either side to win a decisive victory. A victory by Iran would undermine global economic and political stability. A victory for Iraq -- an improbable outcome -- would give the secular Baghdad regime an incentive to return to its earlier support for terrorism and pressure on moderate Arab governments, including Kuwait. At heart, then, the Iran/Iraq war poses two issues for American policy: Is one side winning the war? And are there means available to reverse the trend?

Prevent Soviet Domination of the Persian Gulf: For over a century Russian imperial ambitions under czar and commissar have been directed at obtaining a foothold on the Persian Gulf. But for British intervention, Iran would have shared the fate of the Central Asian principalities that were conquered by Russia in the 19th Century. But for American intervention in 1946, the Soviet Union would have annexed the Iranian province of Azerbaijan in pursuit of the historic Russian objective of dismembering Iran. The Soviet occupation of Afghanistan in 1979 was not an aberration. Historically Iran has always been the ultimate prize, and Soviet control of the Gulf has always been the ultimate danger.

In what sense does the threat to Kuwaiti shipping involve these three vital American interests? In December 1986, shortly after learning of the clandestine sale of American arms to Iran, friendly Kuwait -- closely associated with Iraq -- asked the Soviet Union and the United States to help protect its shipping in the Gulf. The Soviet Union responded by leasing three tankers to Kuwait, implying that it would protect their free passage. Some months later the United States agreed to put 11 Kuwaiti tankers under American flags. Simultaneously it beefed up its fleet at the mouth of the Gulf.

The administration's advocacy of freedom of navigation is prudent. But the reflagging of Kuwaiti ships amounts to overt support of one combatant, Iraq, in the Iraq/Iran war. It is by its nature an open-ended commitment. A military tilt toward Iraq would make sense only if there were a new, clear and present Iranian threat to navigation in the Gulf and if the action promised some decisive result. Neither the nature of the naval war nor the statistics on ship losses support such a conclusion.

Since the beginning of the naval war in the Gulf in 1981, some 320 ships have been attacked, roughly 220 of them by Iraq. (Very few of them have actually been destroyed.) During 1986, 100 ships were attacked by both sides at a ratio of 3:2 in favor of Iraq. But since Iraq also attacked some of Iran's oil terminals and loading facilities, its interference with the global oil supply almost certainly has been greater than Iran's. In any event, none of the attacks by either side seems to have had a measurable impact on the global oversupply of oil or on oil prices.

Thus far in 1987 there have been about 50 attacks with Iraq doing more damage, along the same pattern as last year. Partly in compensation, Iran has been reported ready to install Chinese missiles capable of threatening shipping in the Straits of Hormuz, the choke point in the Persian Gulf.

Three conclusions emerge:

The odd aspect of the crisis is that nothing significantly new has happened. The rate of attacks continues about at the level of last year, when no Western country -- including the United States -- bothered to protest, and the United States was clandestinely shipping arms to Iran. The best evidence that there is no new threat is that ship insurance rates for the Gulf have not changed appreciably in 1987.

If the United States is upholding the principle of freedom of the seas, why does it protect the side that has so far interfered most with shipping? On the other hand, a parallel commitment to defend Iranian-bound vessels, though it would bring about a paper symmetry, would in fact favor Iran, by taking away one of Iraq's strongest weapons -- the ability to disrupt Iran's biggest hard-currency source, its oil exports. In short, America's justification is not consistent with its actions -- a sure course for domestic discord when the going gets tough down the road.

If the United States is extending protection to Kuwaiti tankers in order to affect the outcome of the war -- the only rationale that makes sense -- it must be prepared to face the implications of its actions. A military challenge to Iran in the absence of a clear provocation cannot be terminated as long as the naval war in the Gulf continues without serious prejudice to America's already battered prestige. Indeed it stakes American military prestige to some extent on the outcome of the land war.

Escorting 11 ships will not decide the naval war, nor will ending Iranian attacks on shipping decide the Iran/Iraq war on land. America thus risks being drawn into an expanded military role that cannot be decisive. The United States must not repeat in a new theater of operations the mistake of doing enough to get involved but not enough to prevail.

Some defend the reflagging as a counter to the lease of Soviet tankers to Kuwait. Others even more ambitiously see it as a test case for possible U.S.-Soviet cooperation on Third World issues.

Had the United States taken protective measures on behalf of moderate Arab states at the beginning of the Gulf naval war it might, perhaps, have headed off a Soviet presence in an area long considered a vital Western strategic interest. But after the fait accompli of Soviet involvement, reflagging Kuwaiti tankers does not stop the Soviets, it joins them. So the action may well send the wrong signal. Especially in the year that ransom payments to Iran have become public, reflagging will seem to some as an American propensity to yield to blackmail. If this becomes a pattern, we could see a vicious circle of multiplying Soviet involvement and multiplying American commitments.

The argument that the possibilities of East-West political cooperation can be tested in the Gulf deserves an even closer look. Perhaps the United States and the Soviet Union share the short-term interest of preventing an Iraqi collapse. But their long-term interests surely diverge. The Soviet Union has historically encouraged the disintegration of Iran. The United States' goal, on the other hand, should be to preserve Iranian territorial integrity and to strengthen its independence while at the same time confining it within its national borders.

The current hostility between Iran and the United States is real but unnatural. While the United States has for now no other choice than to resist the spread of Iranian fundamentalism, it can have no conceivable design on Iran's territorial integrity.

A wise American policy will seek to prevent the defeat of Iraq without tacitly allying itself with the Soviet Union. Perhaps Iran will give the United States no option other than confrontation. But America must not compound the mistake of selling arms to a country whose victory would harm American interests by edging toward belligerence on the other side in circumstances that increase the Soviet threat to the Gulf.

In sum:

The United States must defend freedom of navigation in the Persian Gulf against a clear and present threat to the interruption of shipping, whichever side poses this challenge. It should do so preferably in concert with its allies, but alone if necessary.

Military action against Iran -- direct or indirect -- can be justified only if there is a significant escalation of Iranian attempts to close the Gulf to the free flow of oil.

The central goal of the United States should be to bring an end to the Iran/Iraq war. In pursuit of that goal, the cease-fire efforts in the U.N. Security Council should be pressed, including sanctions against the combatant refusing the appeal. These sanctions cannot be effective unless all members of the Security Council cooperate.

To give the cease-fire efforts a chance, the United States should ask for a 60-day cease-fire in the naval war in the Gulf and suspend the reflagging of the Kuwaiti ships while that cease-fire holds.

The United States can and should stand for an end to hostilities. It can and should give nonmilitary help to the side whose defeat would damage American interests -- at the moment Iraq. Increasing American firepower in the Gulf does not answer these concerns. What the United States must not do is to engage in belligerent acts without knowing what it seeks to achieve.