Three years ago professional forecaster Marvin Cetron warned about an Islamic revolution in Iran. Nobody listened.

Today, on completion of a four-year study, he sees: Japan dropping badly in world status because it is losing business to resource-rich China; Israel going heavily conservative and ever more nationalistic; Saudi Arabia falling in a revolution unless we give massive support; economic disasters striking India and Poland.

He is afraid no one will listen again.

"People come around to us now and say, 'Hey, you were right on Iran. How 'bout that?'" And he shakes his head.

"One member of Congress told me he can't handle a crisis before it becomes a crisis. In other words, he's reactive.All we do is react to what happens to us."

At the very least, one would think, the government could have tightened the guard at its Tehran embassy.

Cetron, an industrial engineer who runs Forecasting International in Arlington, wants to give seminars in his techniques to government people. He thinks it might give added weight to the forecasts. In the past he has done work for the armed services and other government agencies. The present survey is for a group of 25 major industrial firms.

How does he work? Is it just speculation?

"Our technique is so accurate it's scary. We tested it out by applying it to the past, like 20 years ago. It was right on the button. We even came up with the Cuban revolution."

A couple of years ago he did a study on the economic future of America for NASA. Before that, there was a $90,000 survey on Sweden, as a bell-wether nation, for the National Science Foundation. Other government and private agencies have asked his firm to give this or that area its special treatment.

What they get are not startling statements pulled out of a hat, but a form of organized speculation based on the various possible interpretations of known facts.

The system is a combination of statistics and intelligent judgment. It is all a matter of breaking down a situation into factors, analyzing and weighting them, subdividing them into ingeniously simple categories. Cetron and his top assistants on this project, Dr. Anne Nelson and Sharon Sugarek, have invented a special language to help clarify things.

"We have what we call vital signs for a nation, just like a person's vital signs: their welfare figures, how they take care of injustice, the treatment of dissidents, political stability and military security, and their self-image, and so on. We integrate all these which affect them, and finally we run this picture past possible events, scenarios, and we see what happens to the picture."

Juggling all these factors sounds like an impossible nightmare, until you learn that they are turned into numbers -- say, the effect of food on population is 2 on a scale of 10, but the effect of population on food is 9 -- which are assigned to them by Cetron's large staff of people competent in a variety of areas.

"Take a little thing like corn," Cetron said. "You get sugar from corn, and it's cheaper and even sweeter, and you say what's the big deal? Well, it is a big deal: it dropped five countries into what we call the Fourth World, which means it's not only underdeveloped like the third World, but also it has no natural resources that the rest of the world wants."

An exception was Jamaica, which lost its sugar market to corn, but happened also to have bauxite and so was still in the ballgame.

Cetron collects his basic information from many sources, from the World Bank and Brookings Institution to congressional reports and newspapers.

"The problem today is that we have too much data -- we have data pollution -- and not enough use is being made of it."

His reading of the Iranian situation, which he forecast in January 1977 as a possible event ("Islamic radicalism and 'holy war' for Moslem unity sweeps Mideast") goes like this: "The shah tried too much too fast, with women's right and civil rights and other Western-type reforms. Ataturk did it in Turkey, but he went much slower. The biggest problem was that the shah stopped paying the mullahs, the church leaders. We call it bribery, but this is an accepted part of economic life in that part of the world."

He is not optimistic about the immediate future in Iran and other countries with large numbers of Shiite Moslems "because their self-image is so high that they'll die for their beliefs. Also we're perceived badly by them; they don't think we'll fight."

So the proportion of Shiites in the population has become one of Cetron's criteria for Middle Eastern countries. Another is the gap between the top and bottom tenths of the economic scale.

"If a man's head is in the oven and his feet are in the refrigerator, his average temperature may read normal, but he's obviously in bad trouble. Now in Saudi Arabia today, there's a 30 percent gap and worse. People are uptight. Also they're not paying off the mullahs. So we find Arabia extremely unstable."

Another key statistic that Cetron calls absolutely vital to determining a nation's volatility is the number of a unemployed males between 18 and 28.

"These are young men who perhaps have come out of the country and got some education and moved to the city, but have no job. They can't go back and be a shepherd. They have nothing to lose."

One is reminded inescapably of the Iranian "students."

Some of the other "events" that were run through the computer to see "what if":

Dissolution of NATO. OPEC oil embargo against Israel's supporters. Nuclear capability in Iran and Libya. Dissolution of OPEC. Soviet Union becomes major oil importer. Collapse of parliamentary government in India. Eastern European nations breaking away from Soviet bloc.

He had 32 of these speculative scenarios, and he had analyzed the probable effects of each one on the world powers.

Some of the changes in national status, based on vital signs, that he sees for the last fifth of the century: The United Kingdom rises from 5th to 1st place, and West Germany drops from 1st to 3rd. Japan goes from 2nd to 14th, Israel from 11th to 20th, India from 14th to 21st.

In his studies, Cetron has picked up a remarkable assortment of insights about how the world operates. Here are a few:

"The transfer of technology is not easy. You can't go to a guy who uses an ox or maybe his wife to plow and give him a Beethoven tractor. (That's one of those two-story combines with air conditioning, a toilet and a stereo so you can play Beethoven while you plow.) Also, you can't give Fourth World countries money."

"You have to consider some of these huge multinational enterprises like countries. Some of them are richer than all but the top four nations in the world. And they have more political clout than most countries. Not that this is all bad. It can be a stabilizing influence."

"Nigeria may be a major problem to us because of its large Islamic population. This thing isn't going to end with Iran, you know."

"The problems between North and South are greater than the problems between East and West."

"If a country doubles its military salaries in two years, you know there's a problem."

"One of our worst problems in America," he says, "is our lack of cultural sensitivity. Too often we see everything from our own perspective. For instance, we are shocked by coups. Yet some countries routinely change government by coup and are still stable. We have to learn that a lot of the people out there are very very different from us."