This suspense film began with wondering

When Frederick Forsythe writes a book, a movie is sure to follow. His first novel was called "The Day of the Jackal." The film version, released in 1973, was major hit starring Edward Fox. Then came "The Odessa File ," which made less of a showing when it was adapted to the screen, with Jon Voight in the leading role.

Just now, Forsythe's third book -- "The Dogs of War" -- is being filmed by United Artists, with Christopher Walken (of "The Deer Hunter" and "Annie Hall") in his first starring role. And Forsythe recently visited Hollywood to bang the drum for his latest novel, a fat best-seller called "The Devil's Alternative," which could end up as a lengthy movie or perhaps a TV miniseries.

When Forsythe plans a novel, the plot always comes first, before characters or messages or themes. In 'Jackal,' he told me recently over lunch, he wondered how about intrigue in France. In 'Odessa,' "I wondered how you would track down a missing Nazi. The first stage, in all of my books, is to dream up the story."

It was the same with "The Devil's Alternative," the British author's latest novel. "It all began when I got to wondering: What would happen if a group of terrorists took over the world's first million-ton oil tanker and held it for ransom? After that, it was just a question of filling in. Would they be left-wing or right-wing terrorists? What would their motivation be? I ended up with a justification for each aspect, and subplots began to emerge -- a global canvas with power politics, espionage, and everything."

Inventing the story is just the first step, however. Then comes an enourmous amount of research, to ensure the credibility of every element of the novel.

"I try to keep everything probable, or at least feasible," says Forsythe." I don't go in for science fiction. If I write about a satellite system that can photograph any spot on our planet with amazing accuracy, it must exist -- or, beyond doubt, be about to go into production."

Forsythe does this research by himself, with no assistants. He has three main sources of information. Most important are his contacts in various professional, political, and scientific circles. Also valuable are his own personal observations; if Forsythe describes the decor of a restaurant, it's safe bet that he has been there and taken notes on every detail. And finally, there is publicly available documentation. "More is available than people usually think," says this former journalist, who hasn't forgotten how to dig up an obscure fact when he needs it.

"The Devil's Alternative" is crammed with unusual information and unexpected details, right down to the style of furnishing in the Politburo meeting room in the Kremlin. At its worst, the book is top-heavy with needless minutae, which become especially burdensome when they creep into stilted dialogue passages. At its best, the novel carries an uncommon sense of authenticity. It may be far-fetched at times, but it's rarely unbelievable.

In any event, Forsythe takes his factual excursions very seriously. "Some things might not matter to the ordinary reader," he says, "but they're a point of pride to me. Some people really know about tankers, for example, and they'll be looking very carefully at my tanker details. They won't know much about the wheat information in another chapter, but the wheatm people will be on their toes. If you're too sloppy to get all these things right, you'll eventually disappoint a lot of people in one chapter or another."

Forsythe considers "The Devil's Alternative" to have been his most difficult book to write, because it deals with the future. "Instead of writing about the recent past, as in my other novels, I was trying to envisage the world as it would be in three of four years," he says. "I was very lucky. I said the Shah of Iran would fall, and I said there would be a female Prime Minister in England , and both those things happened -- ahead of schedule, in fact."

Becoming a journalist was natural for Forsythe, who had planned on that career since his teen-age years. "I always wanted to be a foreign correspondent ," he recalls. "That way I could travel widely and someone else would pick up the ticket. But after 12 years of journalism, I found myself back in London after the war in Biafra, out of work and with very few savings. I decided to write a story that had been on my mind since my years in Paris during the early '60s. I began the novel to kill time and make a little money. I killed the time all right, and made a lot more money than I'd expected. So I never went back to journalism."

After "The Day of the Jackal," Forsythe polished off two more novels in two more years. "Then I felt like some time off, and I stuck to it for five years." During most of that time, though, "The Devil's Alternative" was "gestating" in the back of his mind. "After a while, it began to bug me. So I explained it to my wife, and she asked me why I didn't go ahead and write it." The research took about six months. The actual writing took 44 days. Thus did Forsythe return to the bookstalls and bestseller lists after his long hiatus.

Forsythe has never felt tempted to become involved in the filming of one of his books. "I take the money and run," he says. "Those other guys are professional filmmakers. Let them make the movies. I'll just do my novels."

This aversion to moviemaking extends all the way to screenwriting. For one thing, he says, it's a tricky area to break into. "I've never done a screenplay , and it would be foolish of anyone to invest a lot of money in a first-timer."

But another consideration also looms large. "It tends to be writing by committee. And that's not my bag of beans at all. By Scene 4 or 5, I'd probably present my typewriter and a few pieces of paper to the committee, very ceremoniously, and say: That's a good idea. Go do it yourself."

In sum, screenwriting is an entirely different profession that wouldn't suit the individualistic Mr. Forsythe. "My life is quiet and peaceful," he says, "and I like it that way. I'm not surrounded by screaming producers or directors or stars. I'm surrounded by sheep and oak trees and the hills of Wicklow. And that's much better."