THE ROMANTIC 19th-century notion of the terrorist as a person in the grip of a passion, as an individual making a statement, lingers on to pernicious effect. It nourishes in some quarters an unnecessary psychological indulgence of the act and it keeps people from realizing that in the 20th century terrorism is largely an organized group or state-sponsored and -managed activity. This is importnt because such grops as the PLO and such states as the Soviet Union and its allies -- the principal sources of terror in the world -- have between them resources far surpassing those available to individuals. There was both a PLO and a Soviet hand behind the seizure of the American hostages in Iran. Any attempt to combat terrorism must cope, if not start, with that fact.

The PLO openly conducts acts of terror against Israel and more quietly maintains ideological organizational contacts with killers with other obsessions -- in what Claire Sterling called, in an op-ed article the other day, "the terror network." Do the people who "understand" PLO violence when it is directed at Israelis realize that they are thereby in some measure supporting attacks on others? The PLO needs to be called to account, by its friends, for this connection. The United States, which has linked its acceptance of the PLO to the PLO's renunciation of terror against Israel, needs also to ask that it sever its links with Carlos the Jackal and the Japanese Red Army. Certainly the PLO deserves no credit for attempting to intervene for the hostages in Iran, when its larger role was to help make the terrorists' assault possible in the first place.

There will always be an argument over the Soviet role in particular incidents, but overall it is undeniable that the Kremlin, politically and logistically, gives incalculable assistance to international terrorism. East Germany, Czechoslovakia and Cuba seem to have special sub-functions. Soviet-bloc nations are involved in multiple relationships with the United States and other countries. This makes it difficult to send an unequivocal stop-or-else message. Yet surely much can be done, in this country and abroad, to improve intelligence and counterterror measures adn to raise the political costs to the perpetrators. How strange that Moscow should have gotten a free ride for being the hatchery of international terrorism. How unacceptable.

Should the United States fight fire by fire -- "unleash" the CIA, resume covert operations on a broad scale and even go (back) into the terror business itself? Terror is real: we may not yet have seen its most extreme permutations. Yet a response that blurred the line between terrorism and tough legitimate self-defense could produce excesses that would feed the fire, complicate the search for allies and sow domestic distraction. What is more important, as a first step, is to realize that the old relaxed ways of dealing with terrorism will no longer do. Responsibility for it must be fixed, and new policies, operational and political, must be devised.