One of the urgent inquiries that needs to be pressed now that the hostages are home is whether their seizure was a home-grown Iranian affair -- just one mullah and a bunch of students -- or whether it also resulted in some substantial measure from the workings of an international mechanism or conspiracy.

The question has enormous implications. If the seizure was home-grown, we can briefly curse the Iranian crazies and go back to playing each new case of terrorism as a unique isolated tactical episode. This is the approach inherent in Ronald Reagan's pledge to take "swift and effective retribution" against future terrorists rather than to follow Jimmy Carter's model of "constant restraint." But if what we are dealing with is "international terrorism," as Secretary of State Alexander M. Haig Jr. put it at his first press conference, then a whole new strategy must be developed. Haig indicated what one aspect of this strategy might be by his charge, unprecedented in level and explicitness, that the Soviets have a conscious policy of "training, funding and equipping" global terrorism.

At least one former hostage, apparently meaning to challenge the conspiracy view, said this week that there was "enormous evidence, truly cogent evidence, for the proposition that the people who took us, that captured us, were students, legitimate students."

It will be interesting to review this evidence, and to see how conclusive it is. I have to say that having started out thinking that the burden of proof was on the conspiracy theorists, I now feel that the "just students" school is no less in need of substantiation. Since it seems extremely unlikely, however, that either a smoking gun or an entirely smokeless one can be produced, any inquiry is bound to proceed on a judgmental basis.

There is first and unavoidably a clash of mind sets. Some people believe that the international environment is on balance kindly, or at least forgiving. Or that nationalism or individualism pathology explain most of the terrible things people do to each other. Or that the United States is due pretty much whatever is dished out to it the Third World. Or that the whole notion of international conspiracy is intellectually a cop-out and politically a mask for simplistic anti-communism. Others believe something opposite.On the basis of mind sets, you can play it either way in Iran.

But on the basis of broad political considerations, I see some sobering things:

1) Iranians have long been a known part of the international terrorist "network," or "Interterror," as it is variously called. These are people who support each other operationally and psychologically and whose common purpose is to destroy the American-Western-"imperialist" -capitalist-democratic position everywhere.

2) In Iran, Iraq, Libya, the PLO and, above all, the Soviet Union there exist elements with an ingrained ideological hatred of the United States and with the means to do the United States and its friends great harm.

Notwithstanding their first pronouncements on terrorism, it is not yet clear that Reagan and his aides have gone much beyond picking up on the public's obvious concern with the Iran hostages. Not enough time has passed for a broad-gauged program to be worked out. There is always some risk that a switch of priority from human rights to terrorism, such as Haig announced on Wednesday, will end up providing more comfort than it should to right-wing thugs.

One missing element, it seems to me, is a serious appreciation of the threat that international terror has meant -- and in some cases still means -- for the industrialized democracies of Western Europe and for certain countries on the periphery, such as Argentina. In the hostage incident, we have seen terror used as what seems to many of us a one-shot passing instrument of national humiliation. By contrast, from the 1970s extending into right now, terror has been used in some European countries and elsewhere as a sustained instrument intended to brutalize the leading institutions of the state and to create true chaos. This is not even to speak of potential nuclear terrorism.

Many Americans have something of a child's view of terrorism -- simple, unhistorical, sci-fi. We have not been victimized by it as others have been, and we have a tail image of the beast. What happened in Iran may have been the deepest American exposure so far to a phenomenon rooted not only in individual pathologies and local conditions but in international organizational and political connections, too. We must come to understand that incident far better than we do now.