"ITS A BIT of a leap, yea," says David Lynch, the improbably young and still-more-improbably young-looking director of "The Elephant Man."

Lynch claims to be 33, but he could pass for a prep school student with his floppy, sandy hair and blue blazer. He might not pass for a man who has just been directing John Hurt, Anne Bancroft, Anthony Hopkins, Dame Wendy Hiller and Sir John Gielgud in a $5 million movie.

Lynch came to "The Elephant Man" with only one feature film behind him -- a dard, surrealist comedy called "Eraserhead." He began it in 1971, as a fellow of the American Film Institute's Center for Advanced Studies. He finished it five years later.

"I kept running out of money," he explains. But after a showing at the 1977 Los Angeles Film Festival. "Eraserhead" was picked up by Ben Barenholts, an independent New-York-based distributor. Barenholts said he couldn't afford to advertise the movie. "He just told me, 'David, you're going to have to have a lot of patience,'" says Lynch. So Lynch was patient.

It wasn't hard, he says, since "I never thought the film would be distributed at all." And gradually his patience was rewarded. "Eraserhead" was released in October, 1977, and today, after many small engagements, it has become "one of the top four of five films on the midnight and college circuit," according to Lynch, and "it's just hitting profit."

"I don't know exactly all the things that came together to get me "The Elephant Man,'" he says. "I was in the right place at the right time . . . Freddie Francis, the director of the photography, told me, 'You've got to get thrown in the deep end.'"

He does not appear to have drowned. "The Elephant Man," which opened here Friday, has broken house box-office records in Los Angles, San Francisco, Toronto and New York, and Paramount Pictures is acting like a studio with a hit on its hands. And Lynch is acting like a man with a career on his hands.

At first, though, his big break looked like a dubious proposition. In 1978, the obvious vehicle for a movie about John Merrick, the grotesquely deformed man rescued from a sideshow and adopted by London society in the 1880s, was the hit Broadway play by Bernard Pomerance. When Mel Brooks optioned an original screenplay on the same subject -- and also called "The Elephant Man" -- by Christopher DeVore and Eric Bergren, the Broadway producers immediately sued, claiming an economic stake in the title

"When I put myself in their position," says Lynch, "you can't blame them for being upset." But titles cannot, per se, be copyrighted, and this one had already been used widely enough to prompt a Variety headline that read: "Herd of Elephant Men' Storming U.S. Stages." There was even an opera about Merrick (called "John M"), which had been produced in London.

For all these reasons, the lawsuit was settled with Brooksfilms' agreement to disavow, in its announcement and advertising, any link to the play.

"I had never heard of "The Elephant Man' until I saw the script," says Lynch. "I just fell in love with the whole thing . . . . This innocent creature beneath this hideous body was what got me."

The most immediately conspicuous difference between the two versions is that John Hurt, star of the movie, attempts to look like Merrick (in his unmasked scenes), using some of the buldiest makeup ever marshaled behind the cause of creating a human face. In the play, on the other hand, Philip Anglim, David Bowie and the others who have had the role have been content to suggest Merrick's deformity with a few contortions of limb and voice.

But since both versions trace back to the same original material -- surgeon Frederick Treves' account of his involvement with Merrick -- there are conspicuous similarities, including the curious use of Madge Kendal, a 19th-cnetury London stage actress, as a principal character in Merrick's life. (Actually, there is no evidence that Merrick and Mrs. Kendal ever met.)

Lynch isn't interested, at the moment, in comparisons or justifications. He still hasn't seen the play -- on advice of counsel -- but he plans to see it now that his movie is out. In the meantime, he specks with the generosity that comes from success. "People who have liked the play have liked the movie," he says. "I think it's going to do real well for the play and real well for the movie."