For the past two years, Michael Crichton has had a pat answer to that unavoidable question "What are you working on?" Casually he replies, "I'm writing the most expensive movie ever made." That is, if it gets made. What exists so far is a new Crichton book, Jurassic Park, which appears in bookstores this month and has been optioned to Universal Studios for $1.5 million, with Steven Spielberg lined up to direct.

But though Crichton's high-tech thrillers routinely make it to the screen—witness The Andromeda Strain and The Terminal Man—his latest work poses special problems. "There were reports that this film could cost $40 to $50 million," says the writer and sometime director, whizzing along the Santa Monica Freeway in his silver Cadillac convertible. "But the animals alone will cost that much. They will be three stories tall and take a year to make."

Jurassic Park weds cutting-edge science to the law of the prehistoric jungle. According to the story line, an array of dinosaurs has been cloned, with reconstructed DNA, by an American bioengineering company building a theme park on an island near Costa Rica. But before the park can open, the computer systems that are supposed to keep the huge beasts behind electrified fences begin to fail, and the dinosaurs run amok among their human creators. The result is a "scary, creepy techno-thriller," says Publishers Weekly, which can "be read as a thought-provoking fable about technological hubris and the hazards of bioengineering."

In fact, Crichton, 48, has included a nonfiction preface in his book that explains to readers that biotechnology, which "promises the greatest revolution in human history," is being pursued by private corporations with little public oversight. Citing such "frivolous" uses of the technology as the creation of paler, easier-to-see trout or square trees for easier lumbering, he says, "Our species has done a lot of things that were hasty or fall into the look-what-I-can-do category. This impulse science, much like impulse buying, needs to be stopped." Such unexpected observations are almost to be expected of Crichton, who, among his other accomplishments, boasts a medical degree from Harvard. "Michael is truly invigorating to talk to," says his friend, writer John Gregory Dunne. "He has a broader field of knowledge in science and medicine than most writers, and he possesses more common sense than most people I know."

Crichton, who didn't know much about dinosaurs before he began researching this book in 1982, says, "My thinking has changed unbelievably." He is now convinced that the creatures, once considered slow and dim-witted, were in fact fast, agile animals with complex social lives. He has also taken a few liberties in the book to keep the action moving. "Were velociraptors as intelligent as chimps? Did dilophosaurs spit venom? I don't know," he says. But "my basic strategy was not to make up any more than I needed to."

The eldest of four children of an advertising executive father and a housewife mother, Crichton was raised on Long Island amid the trappings of upper-class privilege. Yet he felt the sting of exclusion because of his height. Now 6'9", he was already a gangly 6'7" at age 13, and other children treated him as a sort of awkward, ineffectual dinosaur. As he wrote in his 1988 memoir, Travels, "The older boys sometimes chase me home from school and knock me down.... I am smart, and I am going to show them all."

As a teenager, Crichton buried himself in popular culture—science fiction and Hitchcock movies. When he entered Harvard, a writing teacher criticized his literary efforts as shallow, yet he managed to pay his way through med school by churning out potboilers under various pseudonyms. By the time he graduated, in 1969, he had reconsidered medicine as a profession. "I was a little too imaginative," he says. "People came to me with their symptoms, and I would look for a new disease."

The huge success of The Andromeda Strain in 1969 set him up as a professional writer. But it also put strains on his marriage to high school sweetheart Joan Radam, whom he had wed in 1965. When they separated in 1970, he moved to the Hollywood Hills. His second marriage, to lawyer Kathleen St. Johns, ended because "she wanted to pursue a career," says Crichton. So did his third, to Suzanne Childs, a broadcast journalist turned lawyer. By this time, Crichton was beginning to wonder if perhaps he was part of the problem. "You may think that you are a swell and admirable person," he says, "but how many times do you have to get into a traffic accident before you wonder about your driving skills?"

Crichton met his current wife, actress Anne-Marie Martin, 33, when he was directing Tom Selleck in the movie thriller Runaway in 1984. Married in 1987, they have a 21-month-old daughter named Taylor. Anne-Marie hasn't worked much since the baby's birth, and parenthood has altered Crichton's life as well. "Men are pregnant, too, and women have little sympathy for it," he says. "I think we go through a denial stage because it's a change in status and psychological definition. You're going from a wild and crazy guy, a roving stud-muffin, to Dad."

Making coffee in their Brentwood home, Anne-Marie says, "Michael is very patient and thoughtful with Taylor. He waited a long time to become a father, and he was ready." So ready, in fact, that he was able to break a 19-year cigarette habit because he didn't want the baby to get wind of his vice. "I didn't want her to smell it on me," he says. "Having a child makes you less self-centered, and that's an attractive change."

—Ken Gross, Lorenzo Benet in Los Angeles