SHORTLY AFTER American hostages were taken at the United States Embassy in Tehran in 1979, President Jimmy Carter summoned University of Virginia Prof. R. K. Ramazani, America's leading expert on Iranian foreign policy, to a meeting in the Oval Office. Repeatedly Carter emphasized that the United States was not in conflict with Islam, only the Iranians, Ramazani recalled later.

Carter was right in recognizing the problem, but events have proven that separating the two is not quite so easy. In Islam, politics and religion are inseparable. And in the late 20th century, the Islamic fundamentalism preached from Iran has become the most potent force for discontent and revolution throughout the Middle East.

That force is behind the hijacking of TWA 847, as well as the earlier bombings of the Marine compound and two U.S. embassies in Beirut, and the American mission in Kuwait over the past 26 months. American diplomats throughout the region now work behind tank traps and machine gun implacements in diplomatic fortresses. U.S. citizens often live as recluses.

Five months after the 1983 Marine bombing, Dr. Marvin Zonis, director of the Middle East Institute at the University of Chicago spoke on "The Psychological Roots of Shiite Terrorism" at a State Department seminar. "The message from Iran -- no matter how bizarre or trivial it sounds on first, second, fourth or 39th hearing -- is in my opinion the single most impressive political ideology which has been proposed in the 20th century since the Bolshevik revolution," he said. "This powerful message will be with us for a very long time, no matter what happens to Ayatollah Khomeini."

The killing last week of the 264th American since 1983 by Shiite fanatics was just one of many indications that resolution of the immediate hijacking ordeal will not mean the end of the U.S. conflict with Shiite militants in Lebanon or elsewhere.

In effect, the United States is engaged in a war, perhaps the most trying and unconventional conflict it has ever faced. The opposition is amorphous and diffuse, often without identifiable leaders, members or headquarters.

It is tempting to want to strike back, to confront attackers with conventional military force. But the nature of this war is such that it is not against a state or an area with borders, against which it would be easy to launch air strikes or land assaults. America's foe is a religious movement whose foot soldiers are not confined to a single country or sect.

Yet a state -- Iran -- is the locus of the acts that are so disturbing to the U.S. In 1983, the Reagan administration officially labeled Iran a primary sponsor of state-supported terrorism. It is more accurate to call it state-inspired, for the Islamic Republic's main role is as a model and catalyst.

But beyond the theological and intellectual ties, Shiite fanatics in Lebanon, and elsewhere, do have visible links with Iran. Several leading Lebanese mullahs travel regularly to Tehran. The Iranian Revolutionary Guards stationed in Lebanon's eastern Bekaa Valley since 1982 have provided material and political support for the burgeoning extremist factions. Dozens of young fighters from different groups have received military training at camps scattered throughout Iran. Among them is the current military chief of Lebanon's Amal movement, a youth who between 1979 and 1982 hijacked six planes traveling to or from Libya.

Yet neither the Iranian revolution nor the subsequent war would have happened if there had not been deep- seated antagonism toward the United States. Islamic fundamentalists feel they have not initiated the trouble, but have only responded to an opponent that they feel started it. Their extremism is not for love of violence. Their revolution is against what they feel is foreign domination and encroachment in every aspect of their lives -- symbolized most often by the United States.

One point of consensus among the diverse and disparate Shiite groups, who are often in disagreement with each other on other major issues and tactics, is that they see themselves as having lived under the heel of the United States for 40 years -- since America became the main influence in the Middle East.

Among the most oft-cited American "offenses" against Moslem lands and peoples: CIA assistance to Shah Mohammed Reza Pahlavi in the 1953 overthrow of a nationalist movement led by Prime Minister Mohammed Mossadegh, who had been successfully undermining the royal family's then fragile position.

Nationalists and Shiite fundamentalists came to share a common resentment of what they saw as the Shah's servile attitude toward the U.S.

The U.S. is criticized by militants for trying in the 1960s to manipulate coups in Syria and backing a corrupt king in Libya. In the 1980s, American troops and warships went on the offensive for the first time since Vietnam-against Muslims. The use of American firepower was not because American lives were endangered, but to protect a minority government in Lebanon, one of the Arab world's few democracies.

The U.S. was most recently linked indirectly to a bomb that went off last March near the home of one of Lebanon's most militant Shiite clerics, killing more than 80, although not the cleric. The bombers were reportedly had ties to a group being trained by the CIA.

The long record of fears and suspicions about U.S. intentions in the region were reflected in the manifesto of Lebanon's Hizbollah, or Party of God, released a month later: "Iman Khomeini, the leader, has repeatedly stressed that America is the reason for all our catastrophes and the source of all malice. By fighting it, we are only exercising our legitimate right to defend our Islam and the dignity of our nation. We have opted for religion, freedom and dignity over humiliation and constant submission to America and its allies."

A member of Hizbollah said in an interview shortly after the bombing of the second U.S. Embassy annex in Beirut last September: "We aren't against the American people. We are against oppression and injustice. The fire of Islam will burn those who are responsible for these practices (against Islam). We have been dominated by the U.S. government and others for too long."

American foreign policy in the Middle East, which emphasizes the security of Israel, is also a major cause of the militants' wrath. But the militants' reaction to the U.S. is probably linked more to American policy on other Islamic issues over the past 40 years than to U.S. positions on the Arab-Israeli dispute over Palestine.

Indeed, for more than a month before the TWA hijacking, Shiite militiamen were engaged in bloody clashes with Palestinians. The Shiites' desire for the return of historic Jerusalem is primarily because it contains te third holiest site in Islam, and less because the Palestinians want a homeland. Settlement of the Palestinian question would probably not end the fundamentalists' anti-American crusade.

Nor would dispatching American troops or conquering foreign territory end the conflict. The extremists are now simply too spread out and too numerous for this war to be ended by conventional means.

Yet the hijacking of TWA 847 could serve as a turning point for U.S. policy to end a conflict that is taking a mounting toll in American lives. But the Reagan administration must use extreme caution in analyzing which of three main policy options it adopts: force, sanctions and rapprochement. Otherwise, the U.S. may face an escalation that will make the recent wave of bombings, kidnappings and hijackings seem small-scale by comparison.

Unfortunately, since the attacks began, U.S. policy makers have seen only the violence in the extreme fundamentalist movements without understanding its political roots or its social importance. And the Reagan administration, backed by an angry public according to the television vox pops, now seems intent on sending a message to the militants and their sponsors by using force, probably a quick, supposedly surgical strike after the hijacking is resolved.

What has made Iran such a frustrating conundrum to American policy-makers is the perception that it acts on the basis of passion rather than thoughtful policy. Ironically, the Reagan administration may be in grave danger of succumbing to the same emotionalism that it sees in the fundamentalists.

But the use of force, the first policy option, is likely to be catastrophic in the long run for the U.S. for three reasons. Contrary to public hopes that it will cripple or discourage the movement, the use of force against the Shiite crusaders would only fuel their resentment and commitment, providing new reasons for seeking revenge agains the "Great Satan," as well as creating an even more hostile, anti-American atmosphere, thereby attracting new recruits.

The Shiite extremist has become a Hydra: kill one and two appear in his place. The movements in general have simply become too big to stop by cleaning out a training camp or two, especially with the growth over the past 18 months of a large politicized body of Shiites who agree with the zealots' motives and goals, if not their specific tactics.

As Israel's tragic experience in Lebanon showed, an "an eye for an eye" policy only escalates the cycle of violence into a long-term confrontation. The Shiite militants are truly prepared to die in acts that they do not view as terrorism, but as noble deeds against perceived aggressors in defense of their faith and independence.

The dimensions of the problem are reflected in attempts to pinpoint the groups or individuals responsible. Washington officials last year charged that the Party of God was responsible for the second embassy bombing, which elicited a bitter snicker from an American diplomat on the ground in Lebanon. "That doesn't tell us anything," he said. "Every Shiite in Lebanon is now Hizbollah" -- a statement that was only a slight exaggeration.

The name of Sheikh Mohammed Hussein Fadlallah, the cleric whose neighborhood was bombed last March, keeps appearing in relation to various acts, including charges that he provided or blessed the suicide drivers who bombed the Marine compound. Heated debate still rages over his involvement, but even if the allegation were true, proving it would be difficult since he has repeatedly and publicly condemned hijackings, kidnappings and bombings as "unIslamic" and his headquarters is a mosque.

Unlike most other insurgency movements, the Shiites have often used legitimate institutions as centers of operations. "You simply can't raid a mosque or penetrate a cell centered around an Islamic social center," explained a Gulf state intelligence officer. "And even if you did, you would probably be unable to find anything incriminating beyond a copy of the Koran."

Second, the use of force would also endanger our allies, especially the moderate Muslims who already have problems with fundamentalists at home, in part because of their ties to the U.S. Although the fundamentalist crusade is unlikely to bring down other Muslim governments, it can force them through continuing intimidation and terror to accept their extremist tenets.

Third, the use of force is not foolproof. It carries the danger of defeat that could in turn lead to intervention by the Soviets or others. The basis of the conflict is both political and religious, impervious to the use of force.

The second policy option is economic sanctions, which is unlikely to work because of Iran's oil.

Iran's revolution has proven to be defiantly durable, surviving the drain of earlier sanctions, the challenge from opposition groups both right and left, the trauma of almost five years of war, and the isolation and hostility incurred because of its policies. The reality is that many Iranians, who are already living with meat and petrol rationing, appear to be prepared to endure further hardships to protect their Islamic form of government.

American vulnerability, on the other hand, has never been greater. More than 55,000 American diplomats and federal civilian employees now live abroad in 10,000 different facilities -- not including thousands of American military personnel at bases around the world. The State Department unofficially estimates that more than 1.7 million American civilians live overseas. Merely tightening security, discouraging the use of certain international airports or spending millions to improve diplomatic installations is not going to prevent further attacks.

To end the Shiites' war against the United States, the Reagan administration has no alternative but to defuse the tension with Iran, which has led Islam to its first total "victory" of this century. Most serious militants follow its lead.

As unpopular or uncomfortable as it may be, especially after two major hostage traumas and the rapidly increasing toll of American lives, the United States must then begin looking at the possibility of rapprochement with Iran. It is a bitter pill to swallow, but no other option is effective or practical for a democracy. Equally important, the war is unwinnable.

Just a year ago, I would never have believed I would write these words, after watching rescuers dig through rubble at two American embassies and the Marine compound in Beirut looking for my friends, who were often recovered in bits and pieces. But a certain degree of realism is needed to avoid the loss of more lives, without America's seeming to cave in or concede.

The Iranian revolution is not a mirage, and the elimination of certain radical mullahs or activists will not make it or the crusade disappear. Most Middle East experts now agree that, despite Iran's many ongoing problems, Khomeinism -- or rule based on Islam -- is certain to survive Ayatollah Khomeini.

The United States now needs to demonstrate the maturity and confidence of a superpower. Indeed, the outcome of this confrontation with Muslim extremists may depend more on the political initiative by the United States than on the success of Iranian propaganda and the training of suicide commandos at Iranian bases.

Rapprochement will not be quick, or easy, especially for a nation where elections are held every four years. It will not reach fruition during the Reagan administration. And it will probably not happen during the lifetime of Ayatollah Khomeini. But that does not mean that the United States should not position itself by laying the groundwork earlier, which also might help save American lives during the period in between. The alternative is continued conflict and possible further escalation and higher death tolls.

And there are some hopeful signs. "No matter how virulent their rhetoric, the Iranian leaders have finally come to believe that the very survival of their revolution will be in jeopardy if they fail to cope with mounting domestic political and economic pressures by breaking down the walls of their international isolation," Prof. Ramazani said this week.

In fact, Iran is moving to end its isolation. This year economic ties with Europe have almost returned to pre- revolutionary levels. Japan and West Germany are now among Iran's main trading partners. Behind-the-scene contacts have begun with western states as well as Islamic rivals, including the Saudi foreign minister, who visited Tehran last month.

Iranians have also occasionally allowed pragmatic considerations to overshadow attempts to export their revolution, including not closing the strategic oil lanes to the West through the Strait of Hormuz, comparative restraint in responding to Iraq's aerial strikes on tankers ferrying oil from Iran, and the ongoing, if troubled, relationship with other Muslim states in OPEC. The Iranians also did not retaliate when the Saudis, aided by U.S. AWAC aircraft, shot down one of their planes in mid- 1984.

The major pragmatic consideration for Iran and the Shiite extremists is that the war with the United States is unwinnable, even though they can wreak havoc and destabilize governments along the way.

During the rapprochement process, neither side need "succumb" or lose face -- as important a factor to a comparatively young American nation, expecially after the Vietnam War, as it is to the ancient oriental Muslims. No one need apologize or acknowledge fault since neither side can alter the past, or bring back the dead.

The United States could relay quiet messages through intermediaries that it recognizes the Islamic Republic of Iran has a wide base of support, and that the United States has no intention of repeating the CIA-sponsored operation that restored power to the shah in the 1950s -- which would be folly anyway. Such messages would go a long way toward easing the tension.

Sending a message to Iran would also deal with what is at the core of the conflict and what the militants want from the United States: They are seeking respect and independence on equal terms instead of being looked at as client states or as pawns in bipolar games. They feel the United States is a current and future threat because the Americans have a record of intervention. They use terror since it is the only effective weapon that an emerging movement can use to challenge a superpower.

Precedents for rapprochement do exist -- with the Soviet Union in the 1930s, after thousands of American troops, along with forces from 15 other nations, failed to stamp out the Bolshevik movement in Russia after World War I; and with China in 1972, after 23 years of a cold war, broken by two "hot" wars with Asian communists.

The theocratic regime inran, which has consolidated its hold on power, is now more secure than during the era when Carter attempt to improve relations to help end the United States' first hostage crisis. Indeed, some Iranian leaders have even hinted at a willingness to begin contacts with the West again. In a speech to the Iranian parliament, Foreign Minister Ali Akbar Vellayati said last year: "The world is determined on the diplomatic scene. If we are not present, it will be determined without us."

The stakes are too high, the alternative too deadly, for the option of rapprochement to be discarded simply because it means acknowledgment of Iran, a former client state turned hostile, as a major new dynamic force. The goal must be to channel the growing destructive energies behind the Islamic Republic and the many arms of the crusade into a constructive form.

As Ibn Khaldun, a famous 14th century Muslim philosopher, wrote: "Man's distinguishing characteristic is the ability to think . . . and through thinking to cooperate." The Koran itself demands of the faithful: "And if they incline towards peace, incline yourself also towards it."