Bob Zemeckis is bushed.

He's been ambushed (by studio advertising departments), bushwhacked (inadvertently, by his friend Steven Spielberg) and sent to the bush leagues (by the conventional wisdom), and now, after directing nonstop for three years to work off five years of bad luck, he's just plain tired.

"Once 'Romancing the Stone' was successful, there was a lot of pressure to work right away," he says of last year's surprise hit. Because steady work "is it, this is the dream, this is what you wanted to do all your life. And that's what I did."

His whole body yawns. With his long limbs dangling over the edges of the love seat, his belly suggesting itself beyond the belt of his black jeans, he looks like a spider filled to contentment with a bluebottle fly.

He has spent the past year and a half working on "Back to the Future," which had its difficulties. The star, Eric Stoltz, was replaced five weeks into the filming, at a cost of $3 million; the new star, Michael J. Fox, had to shuttle between "Back to the Future" and the set of his TV series, "Family Ties." The postproduction schedule was accelerated.

The movie opens today, and unless everyone is wrong, the pressure on Zemeckis will not stop. Sid Sheinberg, Universal czar and Spielberg's mentor, thinks it's going to be a huge hit. The buzz around Hollywood is that it might be as big as "E.T."

Forget it. Bob Zemeckis is taking a vacation.

"If you only do movies, you don't experience life, and then you don't have anything to draw on," he says in a Chicago accent of bony consonants and whining vowels broad enough to drive a wheel of Wisconsin cheddar through. "So you find yourself making movies about movies, or things you've seen as a kid. I absolutely don't want that to happen."

His wife, Mary Ellen, will have their first child in December, and Zemeckis will take off at least till January. Although it's hard to imagine him doing such a thing, he will stop and smell the roses.

"The one thing I do believe," he says, "is that you can control your own destiny."

For years he was the troublesome kid brother in the film community's "USC Mafia." He and his writing partner Bob Gale were inducted as blood members about 10 years ago by director John ("Red Dawn") Milius, who had graduated from the University of Southern California's cinema school a couple of years earlier. "They came in my office at Goldwyn, and they were just crazy, they were just raving wildmen," says Milius.

"When I was at American Independent Pictures doing 'Dillinger,' they had a project called 'Rape Squad,' and I offered it to some SC guys, and nobody wanted to do it. They would say, 'I want my directing debut to be more prestigious.' And then these guys came along, Z & G -- 'Rape Squad' would have been an A movie for them!"

"John has a real pride in, as he calls it, 'The Long Celluloid Line,' " says Zemeckis. "He considers USC to be like West Point." Milius had arm patches made for the three of them, with their motto, "Social Irresponsibility," translated into Latin on a coat of arms.

Zemeckis got to Milius with his "calling card," a prize-winning student film called "The Field of Honor." "It was about some guy who was released from a mental institution and goes around and kills a bunch of people," Zemeckis says, laughing uproariously. Milius loved it, and so did Spielberg. The two Bobs, as they're known, were in business.

"Thursday nights we used to go shooting together," says Milius, "and on the way to the trap range there's this place Tommy's. Steven had this cheap Super 8 camera, and he had all these films of us eating at Tommy's and covering ourselves in chili and throwing up on the car, doing Bigfoot imitations, wonderful stuff. Great howling mad evenings out there at the range, out of which came '1941.' "

Originally titled "The Night the Japs Attacked," "1941," written by Zemeckis and Gale and directed by Spielberg, and executive-produced by Spielberg and Milius, would go on to become famous as Spielberg's only flop. Despite some wonderful scenes, what you remember about the 1979 film is some guy falling into a vegetable stand for the 11th time. "The script was shot, and then some," says Zemeckis. "There was a lot more in the way of action and effects and broad comedy. And then what happened was it had to be trimmed into a two-hour movie, and a lot of the thrust of the original story took a secondary position.

"But I'm still really proud of having written scenes that had Toshiro Mifune, Christopher Lee and Slim Pickens in them."

The failure of "1941" didn't stop the Spielberg juggernaut, though; nor Zemeckis and Gale, who became Spielberg prote'ge's when he was becoming the most powerful man in the film business.

For example: While they were preparing "1941," they bounced the idea for "I Wanna Hold Your Hand" off him. Spielberg had lunch with Sid Sheinberg the next day. And by the end of the day, Zemeckis was directing his first feature.

Or: Milius and Spielberg were sitting around in an all-night brainstorming session. "We'd seen 'The Sting,' " Milius recalls, "and I said, 'You know, these guys in 'The Sting,' in a John Ford movie Henry Fonda would've come up and said, 'Get out of town.' And here they are making a movie about them. So let's make a movie about a person who's just hideous, the worst person in society -- the used-car dealer." The result was the black comedy "Used Cars," written by Zemeckis and Gale, directed by Zemeckis.

Both got terrific responses from preview audiences.

Both flopped.

"Let me say that the marketing on my earlier films was certainly not as well coordinated as it is now," says Zemeckis. "A lot of money wasn't spent. Then again, if there's a movie that people want to see, they will find out about it, regardless of the marketing and advertising."

Whatever the reason, the hot young writing team of Zemeckis and Gale hit a change in the weather.

The script they wrote right after the failure in 1980 of "Used Cars" was "Back to the Future." "We had written this cynical dark comedy, and we said, 'Let's do something completely different, something soft and sweet and full of wonder and fantasy.' " The project was developed by Frank Price, then at Columbia, who decided not to make it. As did every other studio. "We ran around all over town trying to peddle it," remembers Bob Gale, "and everybody said, 'This is a real nice movie -- we don't want to do it. It's too nice. Take it to Disney.' We took it to Disney, they said, 'Aw, gee, this is too risque' for us.' "

"The industry had very quickly cooled on anything we had written," remembers Zemeckis.

They still made a living writing, they still had deals, still had at least one person at each studio who would listen to them, but nothing was happening. A horror movie fell through at Filmways; a gangster movie fell through at ABC Motion Pictures. "I got married, did a lot of traveling," Zemeckis says. "I was going to say I'm kind of glad my first two films weren't wildly successful, but I'm not. It was a depressing time. Still, I got a chance to experience life, just live a lot of life." And the only person who wanted to make "Back to the Future" was Spielberg.

"I realized that I had to establish myself as a director out from under the wing of Steven," Zemeckis says. "I said, 'I think if we do another movie together and this one flops, we're gonna have very little credibility left in the industry.' " So instead, Zemeckis took Michael Douglas' offer to direct "Romancing the Stone" from someone else's screenplay.

The film grossed $80 million.

"I was in a position where I could do anything I wanted," Zemeckis says. "All these scripts were coming in, and there was a lot of pressure to do something, and you're able to make a lot of money, and nothing really clicked. I kept saying, 'If this is my dilemma, then the one script that I never really could get out of my mind, the one script that I worked the hardest at getting set up and never could, was 'Back to the Future.' "

So he brought it back to Spielberg to produce. "I wasn't sure if I wanted to do another movie with Steven yet, but I felt that since Steven was the only true fan of the movie, it was only fair to do the movie with him," Zemeckis says. He had, after all, directed a hit. And that's how you make your hit in the USC Mafia.

Among the 40 students in his class at USC film school, Bob Zemeckis found another whose taste in movies was almost identical, and when he found out that Bob Gale also owned a sound-track album to "The Great Escape," destiny spoke to him.

And like Gale, who hailed from St. Louis, Zemeckis is a son of the Midwest, from Chicago's South Side. Half Lithuanian, half Italian; son of a construction worker. He got hooked on movies when he saw "Bonnie and Clyde," worked in a small commercial film house while he spent two years at Northern Illinois University, learned a few tricks making industrial films, used company equipment to make a short film set to the Beatles' "Golden Slumbers" that got him into USC.

"While I was in high school, I heard Jerry Lewis talking about it on the Johnny Carson show," Zemeckis says. "He used to be a guest lecturer or something. I was sitting at home in Chicago and I couldn't believe what I was hearing. I had no idea that there could possibly be a university where you could go to college and learn about movies."

It was just before the era of the film school superstar directors. USC alum George Lucas was in production on "American Graffiti," UCLA's Francis Ford Coppola was making "The Godfather." Film school was still a peculiar thing. "My parents were concerned that it was an impossible feat to break into Hollywood," Zemeckis says. "Not only was it 2,000 miles away, but it was also this thing of mystery. It would've been very difficult for me to go out to Hollywood cold turkey, but it was easy to do under the guise of still being in college."

They were 40 kids, mostly men, going each day to the same classes, "like going to a military academy," Zemeckis says, and all crazy about movies. Staying up all night around the editing tables, debating the big new movies: "A Clockwork Orange," "The Wild Bunch." And then a big breakfast at The Pantry, a 24-hour-a-day eatery without a lock on the door that, according to legend, has been open continuously for 60 years.

He and Gale graduated in 1973 and devised a three-pronged attack on the industry. They started writing scripts, making contacts and trying to break into the exploitation film business with "Bordello of Blood," about "a whorehouse full of vampires," Gale says. They wrote teleplays for "Kolchak: The Night Stalker" and "Get Christie Love," unproduced scripts for "McCloud." When Universal Television offered them a seven-year contract starting at $50,000 a year (plus residuals), they turned it down but used it for leverage to get a motion picture agent.

Prong 1 turned out to be "1941." Prong 2 turned out to be Milius and Spielberg.

Prong 3 never panned out. "Bordello of Blood" was never made, although there is always hope.

Zemeckis has an expansive, hale-fellow manner, but what he reminds you of most is the kid you grew up with who was always taking the backs off of clocks. He loves to talk about the miniature work in "1941," the "Columbo" episode Spielberg shot with only a 20 mm lens, the mechanics of Spielberg's camera work in the drinking scene in "Raiders of the Lost Ark," and he approaches the task of screen writing the same way. "I like movies with tight storytelling more than anything else," he says. "I don't like movies that are loosely structured. My favorite directors are Hitchcock and Capra, and those guys are very conscious of story."

When Zemeckis and Gale are writing a movie, they put every scene on an index card, starting with the ending, then working backwards. When they're finished, they put all the cards on a bulletin board. "It's almost like film editing," says Gale. "You see the whole movie laid out a scene at a time." Then they sit down and flesh out the cards, with Gale, the better typist, at the typewriter.

The scripts are built brick by brick, but the spirit is wild, ecumenically irreverent (they bashed Jimmy Carter in "Used Cars" and now twit Ronald Reagan in "Back to the Future"), filled with frantic nerds and mad authority figures. Boring, Zemeckis says, is the worst thing a movie can be.

"We really did spend a lot of time on the script," Zemeckis says of "Back to the Future." "We just wrote and wrote and wrote the script. We really kicked it. We didn't write this script in a week -- we suffered over it. There's not a lot of attention paid to storytelling anymore. I was getting very depressed because it seemed to be getting worse, and then these films started making all this money. We didn't have any scenes in any locker rooms. We didn't do anything in the girls' shower. Gosh, we're in high school in this movie, and we never went into the girls' shower! At one point Bob and I got into this emotional funk and paranoia, and we wondered, 'Is there too much storytelling in this movie?' "

"Used Cars" was one of the darkest comedies around; "Back to the Future" has a real sweetness. "I Wanna Hold Your Hand" poked fun at people; "Back to the Future" has fun with them.

Is Bob Zemeckis growing up?

"I'm less rebellious than I used to be," he says.

"They're not as much fun," says Milius, "now that they're respectable."