Hank Searls wrote the novel "Jaws 2" from an early draft of the script, but he's not quite sure what the movie version will be like. He'll have to wait two months to find out, like the rest of us.

But Searls knows this: that 1.6 million copies of his book hit the paperback racks this week, and ravenous fans are expected to gobble them up to appease a carefully cultivated hunger. At National Airport yesterday, newsstands sold 61 percent of their "jaws 2" stock in the first four hours

For Gerald Green, the suspense is fairly well ended. "Holocaust" - for which Green wrote both the television script and the novel - is now a part of history. Bantam Books estimates that a million copies of the novel were sold in the first three weeks after it was published. It has gone back to press for a total of 10 printings, nearly 2 million copies. Last Tuesday alone, Bantam Books shipped out a quarter of a million copies.

"Jaws 2" and "Holocaust" are part of the most recent development in a long-term, shifting relationship between the printed page and the screen - movie or television - that began with pictures being made out of significant books like "Gone With the Wind" and has evolved to the point where publishers are trying to make significant books out of pictures.

For the leisurely reader, attuned to the narrative art from Homer to Hemingway, today's paperback rack must look like The Invasion of the Bookoids - literary mutants that look like, feel like and sometimes read like the real things. Actually, it is an invasion and it isn't - or sometimes it is. Above all, it is an example of American ingenuity squeezing an idea, a property for every way it can yield a profit. It is also, in all likelihood, the wave of the future.

The frustrations, for the writer, of making a film out of a book are well-known by now; novelist Ross Thomas sums it up succinctly: "Sometimes they just jack up a title and put a new story under it. . . . The novelist is completely at the mercy of other people."

In recent years (let's say, since 1966, when Issaac Asimov made a novel out of the script for the film "Fantastic Voyage" that sold 1.675 million copies), novelists have been learning the rewards (financial) and frustrations (artistic) of trying to move a story from the screen to the page.

A few years ago a standard rate for a potboiling novelization was a flat $1,500 per book. Payments have escalated sharply since then, and the high end may have gone into what the trade coyly calls "six figures" - anything over $99,999 and under $1 million.

Publishers and writers alike are reluctant to give hard figures (why tell the competition?), but it probably is safe to guess that a good job (the kind for which six months are allowed rather than six weeks) earns between $25,000 and $50,000. Some writers get royalities in addition to a flat rate, and one lucky author - Peter Benchley of the first "Jaws" - is being paid royalties for the use of his characters in "Jaws 2".

When it works, the financial rewards are obvious - they translate into sales figures of over a million copies for such books-from-movies as "Love Story," "The Sting" and "Days of Wine and Roses." But it's not automatic; the success of the novelization depends very heavily on the success of the film.

Bantam, the publisher currently running up numbers on "Holocaust" and expecting to do it on "Jaws 2," has "many more novelizations that don't catch fire than those that really score big," according to a company spokesman.

One recent title of this kind was "Blue Collar," which did not succeed either at the box office or on the paperback racks. The verict is not in yet on "Casey's Shadow," but early returns seem unpromising. "Pretty Baby" was publsihed in February with "less than spectacular" sales but has now begun to move with the release of the film, starring Brooke Shields as a 12-year-old prostitute, and the beginning of controversies over it.

Traditionally, established writers have been reluctant to handle novelization of a script, partly because they prefer to work with their own ideas and partly because this kind of writing has been low in prestige and in payments. This is beginning to change.

Searls said he agreed to do "Jaws 2" partly because he was curious: "This will be my 13th book, and I was interested in finding out what effect the tremendous hype it will receive would have on the book's sales compared to other books I have written."

There was a touch of amazement, a slight hesitation in Searl's voice as he described some unusual financial negotiations with Bantam: "Most of the money was up front, but they were kind enough . . . they liked the book so much, and they sold book club rights to the Reader's Digest . . . that they renegotiated the contract to give me a share of some royalties I wasn't going to get."

Richard Elman, whose "Taxi Driver" (259,000 copies printed) is generally accepted as one of the novelizations that works best as a novel in its own right, recalls that, "I was writing poetry at the time they approached me and I was very reluctant to give it up. But they were talking a kind of money that I don't usually get, and I had to listen. I decided to take out six weeks from my poetry - that's all the time they gave me - and do it.

"It gave me a chance to reach a lot of people I don't usually reach, and I was even able to use one of my poems as a transition in the novel. It's called 'Dream of Almost Certain Death,' and you will find it in my collection, 'The Man Who Ate New York.' It comes in the novel at the point where he's buying the gun; I thought there was no much happening there and I decided, 'Well, I'll give them a poem to think about.'"

Green wrote both the television script and the novel of "Holocaust" because of two "very persuasive people," he said.

"NBC producer Herbert Brodkin brought me in to write the screenplay, but originally the idea was that someone else would do the novelization. Then Marc Jaffe, senior vice president at Bantam Books, persuaded me to make a novel out of it." Two million books later, Green is glad he did.

Novelization has become such a significant trend in publishing that a special panel was devoted to it last week at the Montreal Book Fair.

One professional novelizer Eileen Lottman who has done a couple of novels from "Bionic Woman" scripts and most recently "The Greek Tycoon," discussed the special problems of this kind of writing.

"A script is full of space" such as lighting sound and technical directions she said, "and they want a 300-page novel from a 150-page script that is half empty. You have to do a lot of describing."

On the other hand "the screenplay gives you a skeleton, and it's a real pleasure to write" without having to face all the problems of developing characters and plot that are faced in writing an original novel.

A "minor irritation," in her view, was "script changes while the production of the movie is going on, which could mean a revision for the novelizer."

In "the Greek Tycoon," the heroine of the script was originally blond, then changed to brunette, so that the whole manuscript of the novel had to combed for references to hair color.

Searls didn't have that problem with "Jaws 2." He saw the script, he recalls, "in a rather embryonic stage - I understand it's since been rewritten by other people," and he agreed to write the book after being assured "that I would have carte blanche and they didn't want to stay too close to the script."

The book and movie will begin and end in roughly the same way, he says, but "the rest of the book is pure novel . . . I can't really say how close the novel is to the film."

"Jaws 2" represents a new experiment - an attempt by the publisher to make a novelization a best seller before the movie promotion begins to work on the public.

As part of an elaborate campaign, Bantam has given away 25,000 advance copies of the book, has had Chapter One printed in 18 newspapers in the U.S. and Canada, and has prepared two covers - one showing a shark alone and one showing the shark about to gobble a female water-skier. Returns will be carefully monitored to see which cover sells better.

After one day of sales, Bantam knew that "Jaws 2" had completely sold out in Anchorage, almost completely in San Antonio and in Boulder, Colo. The Krock-Brentano chain in Chicago sold 61 percent of its order on the first day.

Another chain, Paperback Booksmith, jumped the publication date by two days in Yonkers and the Boston area, selling 80 to 100 percent of the stock in five stores during the first 48 hours. These figures have already sent the book back for a second printing, making a total of 1.9 million copies in print.

Until Bantam's double-barreled hit with "Holocaust" and "Jaws 2," the most spectacular recent novelization was undoubtedly "Close Encounters of the Third Kind" - which offers an extreme view of the difference between page and screen as media.

Bill Gross, who edited the book for Dell paperbacks, concedes that the movie's special visual effects were "something we couldn't match in the book" but in terms of clarity - letting the reader know background and what the characters are thinking - the book had advantages.

"At the end of the film," he said, "most people never quite knew what those young men and women were doing standing around like space cadets, and we were able to put that into the book." He also believes it was a mistake to show that aliens at the end, rather than let people imagine them, as a book-reader has to do.

Gross is now enthusiastic about Dell's novelization of a film that will come out next week: "Fist," swith Sylvester Stallone. The novelization, done by Rolling Stone writer Joe Eszterhas, "could have been a best-seller in hardcover," he says.

Time was when novelizations were usually only a sort of souvenir of the movie, a way to make a few extra dollars - like the "Close Encounters" face and body lotion that has been developed as a tie-in with the film. But those days are gone, according to Stan Newman, vice president for publishing at MCA, one of the leading Hollywood people involved in novelization rights.

"Before 'Love Story,' and for a while afterward," Newman says, "most novelizations were just some little book that carried a picture from the movie on the cover. They started to become big business around 1972 or '73, and as they became big business more poeple began to pay attention to quality. The pressure for quality has become greater in the last two years, but the commerical pressure dates back five or six years. Several of last year's biggest selling books were novelizations.

"It's now a fact of life."