MUST TV BE AT THE MERCY OF TERRORISTS?
By John Corry
How does terrorism play on television? It depends. Consider the two-part documentary ''Terror!'' Its point of view is clear; the exclamation point tells us that. Terrorism lies outside the pale; it is something to be abhorred. Ideologists define terrorism to their own ends, while the United Nations, the documentary notes, has been unwilling to define it at all. Most reasonable people, however, need no definition; they recognize terrorism when they see it. Terrorism is a bombing, an assassination, a hijacked plane. It is a violent act in a political context, and it is, as Arthur Hill, the narrator of the documentary, says, ''a part of the world we live in.'' ''Terror!,'' which begins on WNEW-TV/Channel 5 tomorrow night at 9, is something like a compendium of terrorist groups. It says that more than 1,000 groups have claimed responsibility for some 8,000 incidents since 1968, and that more than 500 terrorist groups are operating now. ''Terror!'' looks at some that are, or have been, prominent: the Japanese Red Army, Black September, Provisional Irish Republican Army, Fatah, Prima Lenai, Hezbollah, Armenian Secret Army, Red Brigades. They come from the left and the right. They all kill indiscriminately.