Four years ago, the heartless, oilless Tin Man in the current National Theater version of "The Wiz" was subsisting as a dancer here in Washington when he got the call for his first Broadway audition. The show was "A Chorus Line."

"There was a particular jump at the end of one competition," Clyde-jacques Barrett recalls, "and I knew I jumped well so I did an extreme jump to impress them."

They weren't impressed.

Barrett was eliminated immediately. "But it was encouraging," he says, "because that's when I realized I could compete with the New York dancers..."

His upbeat assessment of that first brush with the big time has been utterly vindicated. In 1976, he landed a job in "Bubbling Brown Sugar," traveling with the show from here to Houston to New York, and has worked fairly steadily-as show people measure these things-ever since.

The Tim Man is nit basically a dancer's role, but Barrett's dancing skills (and the excess of energy that helped lose him that part in "A Chorus Line") are far from wasted. Wearing a costume that looks like an upsidedown garbage pail, a couple of beer cans and a pie plate, he clunks and squeaks and jerks pathetically at first; but as he gathers confidence (and a heart-a fluffed-up red pillow lined with gold lace) he starts moving with an agility that seems startling in such cumbersome attire.

None of this, according to Barrett, comes easily. The costume, actually made of fiberglass, may not be quite as heavy as it looks, "but when you start talking about dancing and jumping around it's heavy," he says. "I have a lot of bruises on me . . . and the ax is real."

The Tin Man is a study in vulnerability, says Barrett. "My whole goal out on the stage is to make this audience appreciate the good aspects of being vulnerable."

And that missing heart, he adds, is a lot less important than they make out. "He has a heart all along-he just doesn't know it."

Barrett has a very small part in the movie version of "The Wiz," and he has seen it twice.

The first time around, he apologizes, "I was too busy looking for myself and so angry with it I had to go back again. I wasn't objective. And the second time, I liked it even less."

Barrett has been the Tin Man for eight months nows-he joined the show during its last stint, at the Kennedy Center-and he is determined not to let those long months show. "I make it a point every night before I go on stage to psyche myself up," he says. "I realize these people who are coming to see me have paid just as much money as anyone else."

His touring regime emphasizes "sleeping, eating and resting," he explains, because he has seen so many actors and dancers get carried away with the social opportunities. "It takes a lot of rest, eating well, vitamins and loving someone in your life,"says Barrett. "Mind you, I don't say being in love because that's a whole 'nother energy level I don't have time for."

One recreation he does have time for is bicycling-to and from work, in Rock Creek Park, wherever. Washington, says Barrett, "is such a good bicycle riding town . . . I like Washington, period. I'd still live here if my profession would allow it but right now New York is the only possible place I can live."

Born in Orlando, Fla., Barrett entered Howard University at 17. He was a music major then, and meant to be a concert pianist. "But I realized by my sophomore year in colege that I refused to spend six or seven hours at a piano every day for the rest of my life."

As a senior, he started dancing, "and it was like a brand new toy for me," he says. "Once I decided this is what I really wanted, I just put my whole head into it."

Although he had found his calling at what most dancers would view as a preposterously late age, Barrett became a professional in near-record time, joining the D.C. Repertory Dance Company (in the old Colony movie theater at Georgia Avenue and Farragut street NW) just a year later, in 1969.

One of the directors of the company was choreographer Louis Johnson. Barrett's job in "Bubbling Brown Sugar" came about as a result of Johnson's being hired to choreograph the show.

People tend to assume his three-pronged name is, well, a recent acquisition. But not so, says Barrett. He has had it all his life. "I don't know what my mother was thinking about. We have no relation with anyone that's French at all."

Until a couple of years ago, he was living and working as just plain "Clyde J. Barrett." But when his mother, a domestic workers in Orlando, came to see one of his shows, she chewed him out about that.

"You know that's not your full name," she told him-and it has been Clyde-Jacques ever since. CAPTION: Picture, Clyde-Jacques Barrett, by Gerald Martineau, left, and in "The Wiz."