Almost every intelligence expert I talked to in Lebanon immediately after the Marine barracks were bombed last October discounted the notion that Islamic Jihad (Holy War) did it. "There is no Islamic Jihad", they said, referring to the entity that has claimed credit for the latest bombing of a U.S. Embassy building in (Christian) East Beirut. I suspected this was the alibi of frustrated bureaucrats who just weren't up to the task of pinning the culprits down.

The truth is quite different.

Treating Islamic Jihad as a real organization, and more particularly as one more example of the world- wide problem posed by terrorists, allows the U.S. government to dodge the stickier task of going after the real culprits.

It is now recognized that the once notorious "Black September" never existed; Fatah invented the dummy corporation to take credit for outrages it committed but could not safely claim. This is not to suggest that Islamic Jihad is Fatah. But the culprits are not the "shadowy" world terrorists both they and some officials of the U.S. government make them out to be. They are more substantial organizations, so substantial they cannot safely take credit in their own name.

Almost certainly they include Iran; perhaps Iran alone played a leadership role this time. For the past year at least, U.S. and other intelligence agencies have monitored Iranian shipments of munitions and even light planes across Syria to various Shia fundamentalists in Lebanon.

In the past the Syrians are believed to have called the shots and provided military expertise. But it is unlikely they played a crucial role this time (except to the extent they may have been politically unable to halt the shipments). Ever since events began running in Syria's favor in Lebanon, Damascus has been working to consolidate its position, and in the past few months this has meant supporting moderate Shias against the fanatics. Moreover, Syria was godfather to the agreement that opened Beirut's Green Line, and the latest attack sorely abused the concept of an open Green Line and the Syrian-imposed peace.

Those who insist there is an Islamic Jihad which is responsible for the bombings usually turn out to be talking about Baalbek-based Shia fundamentalist Hussein Mussawi, the Iranian-supported leader of Lebanon's Hezbollah, a fanatically religious political party which originated in Iran. Last year U.S. intelligence officials told CBS News that Mussawi was responsible for the Marine bombing. However, investigating reporters discovered him to be an inept Koran thumper whom few Lebanese consider capable of organizing any substantial terrorist enterprise.

To see Mussawi as the chief of a real Islamic Jihad obscures the likely use of that term by more responsible parties, in particular both Syria and Iran, that either now or in the past have used Mussawi as a front and a recruiter, while trying to hide their own roles. When President Reagan shakes his head over "the worldwide problem posed by terrorists," without mentioning state sponsorship of these particular terrorists, let alone naming the states, he fosters the same impression.

The ultimate victim -- even the intended victim -- of this new blast may not be the United States. No group will suffer more than the moderate leadership of Lebanon's Shia community.

Most Lebanese leaders insist that any de facto alternative to a peaceful settlement, in particular a splitting of the state into autonomous confessional cantons, is unacceptable. No one protests more adamantly than the secular Shia elite -- future ministers of a central government. An attack by fanatics across the Green Line only reinforces the conviction of many Christians that they should retreat into their own tightly secure canton.

Amal, the Shiite militia, is sometimes accused of the bombings. But Amal's Western-educated leader, lawyer Nabih Berri, is a key minister in the current government and the most prominent of the Shiite moderates. Amal has worked with U.S. officials to provide security for the U.S. Embassy, it has led low-profile raids on the redoubts of non-Amal fanatics to free kidnap victims, and its secular leadership is struggling to maintain its control of the movement, which fundamentalist hellraisers such as Mussawi aspire to take over.

Meanwhile, those who have some knowledge of Lebanon's Shia take too much comfort in the fact that Amal's leadership is moderate, that no group has more to gain from a peaceful settlement, and that Lebanon's Shia are, after all, Lebanese, by which it is meant they are businessmen at heart and practical people.

During the crisis that brought about the departure of the Marines last February, I was with the Muslim militias. Trouble broke out in the southern suburbs of Beirut a few days before the militia took over all of West Beirut. The street fighters were overwhelmingly Amal, and the secular leaders of the militia were clearly in charge. But almost every street fighter wore a plastic-encased photo of Khomeini around his neck. As they advanced through murderous crossfire, sayings from the Koran, plastered on bombed-out cars, exhorted them to welcome death. Similar sayings were scrawled on green bandanas wrapped around their foreheads. When one of them heard I was an American, he said, "Great. Someday I'm going to get in a plane and dive on the New Jersey."

This young man with Khomeini around his neck and murder in his heart was not Hezbollah; he was simply rank-and-file Amal. This is not to say that Amal's leadership is deceiving us with its moderate image. On the contrary, it is to say that these moderate leaders have a tiger by the tail.

But perhaps even more significant for the future is what the people on those streets thought. When West Beirut was invaded in February, papers in this country were full of pictures of the destruction. But the destruction wrought on the Shia southern suburbs the week before was much worse. I was there. The smell of death was everywhere. Families were running for their lives with plastic garbage bags stuffed with their possessions. We ducked into a flour mill where dozens of families had fled for shelter. When they heard I was an American, they began slowly to close in a circle around me, and my mind still races at the thought of what they might have done had I not been with Amal's chief press liaison. "The New Jersey," they shouted. "Look at what the New Jersey is doing to us."

Throughout the southern suburbs, it was the same -- ordinary citizens, bakers, shopkeepers, mechanics, believed that through the week the New Jersey had been largely responsible for the destruction rained on them.

The best evidence is that Maronite and some Lebanese army artillery units were responsible for the destruction I saw. Neither the U.S. fleet nor Marine artillery bombarded the southern suburbs. When Hezbollah snipers fired at the Marines, they answered back with their own sharpshooters or rockets aimed by line of sight. But whether or not the New Jersey was responsible is not the point. What is important is what thousands of Shia across Lebanon believe about the United States.

I fear we have only begun to witness the fruits of their passionate intensity. Blaming what they do on terrorist cliques plotting in cellars beneath bare light bulbs, or imagining them to be some Levantine incarnation of immature Weathermen, simply evades the problem.