WATCHING a Steve McQueen movie in French can be a little jarring. There's something about the soft, melodic sound of the language that doesn't quite jibe with the tough, carousing, motorcycle-reviving image of Steve McQueen.

It jibes even less upon the discovery that the man who dubs the voice of McQueen in the French version of his movies is a slender, refined-looking chap of 50 whose major interests are sculpture and classical music.

"I detest motorcycles," says Jacques Thebault. "I'm even horrified about driving a car. I'm not at all like him. I'm not athletic, I don't like fighting, and I love to talk. Steve McQueen talks very little in his films."

Thebault is sitting in his tastefully decorated apartment on a quiet square in Paris' Montmartre district. He is wearing light blue trousers and a matching jersey. Not a leather jacket in sight.

A serious stage actor who is most at home performing in a Moliere play, Thebault nonetheless enjoys providing McQueen's French voice, and has done so in a dozen of his movies over the past 20 years.

"It allows me to play a part I'd never really have an opportunity to play otherwise. I'm just not big enough, and I don't have the right physique."

There's no reason, of course, that the actor who dubs a voice should look like the actor in the film, and usually he doesn't.

"All that matters is that the voice sounds right coming out of the face," says Hal Brav, an American director who dubs French films into English at a studio in Paris.

But what sounds right coming out of a face may sound very different from the real voice of the actor in the film - especially in the case of John Wayne. For the past 40 years the French have been eagerly lapping up John Wayne movies. But to them, Wayne has never had the characteristic drawl, with its distinctive rhythms, of the Wayne we know.

Raymond Loyer, the 55-year-old French actor who has dubbed Wayne's voice for 30 years, has a low, gravelly voice himself. And in meeting him, I had the impression that he would be a perfect Wayne imitator. With his rugged, square-jawed race, he even looks the part. But on the screen his voice comes across very differently. It suits Wayne's face, but it just doesn't sound at all like him.

To the French, however, that's the way John Wayne has always sounded. Loyer says that sometimes people in Paris recognize his voice when he talks in stores. And once, when he was checking into a hotel in the south of France, the surprised bellboy asked him if he were related to John Wayne.

One of the reasons Loyer doesn't sound like Wayne is that he doesn't drawl. But then, he doesn't really get a chance to; it usually takes more words in French to express the same idea, leaving him less time to stretch out his vowels.

Dubbing has become an important part of the French movie industry. While North American audiences never have been fond of dubbed films, the French have long been avid consumers of dubbed American movies.

In fact, the number of films made in France has been declining over the past 25 years and more and more films shown in French theaters today are foreign. Of these the vast majority are American.

While sophisticated movie audiences prefer to see the original versions with subtitles, the average French movie-goer wants to relax at the cinema and hear everything said in his own language. So as soon as you stray away from the major theaters on the Champs Elysees or the Latin Quarter in Paris, films are usually dubbed. In other French cities films are almost always dubbed.

Dubbing is a complicated process. Not only does the dubbed voice have to express the same idea in the same amount of time, but the dubbed words have to fit the lip movements of the actor in the film. So when he puts his lips together to make certain sounds such as "b" "p" or "m," the dubbed voice also has to make sounds requiring closed lips at the same time.

For example, if the actor in a French film says "bonjour," the English dubbing of this would not be "good morning," but just the abbreviated "morning."

This sound-matching, one of the most crucial aspects of dubbing, is a slow, painstaking task usually worked out here by a specially trained biligual script writer.

To actually fit the word into the film, the director cuts the movie into short scenes of about a minute in length. The dubbing is done a scene at a time, with the actors standing around a microphone in a darkened studio watching the film on a full-sized movie screen.

They watch a scene two or three times in the original version to get a sense of it. Then it is played again a few times without the sound but with the words of the dubbed script moving quickly across a screen right below the film. The actors then dub in the words, reading from the moving script.

To achieve the precise timing necessary for a close-up scene, the actor must pronounce each sound exactly as it passes across a vertical line on the screen. It usually takes about 10 retakes before the scene is successfully dubbed.

Dubbing is, of course, one of the less glamorous jobs in a business where glamor is all-important. Most dubbers are professional actors who would prefer to be taking on real roles on the stage or in films rather than simply filling in the words for someone else.

"I wouldn't sacrifice some important thing in my life for a dubbing role," says Loyer, the John Wayne dubber, who acts on the stage, in films and on television and radio shows.

Still, to a large number of actors who never make it to the big time, dubbing is a way to support themselves in between other assignments. An actor dubbing a lead role in a movie can earn up to $300 a day. It usually takes about a week to dub a film.

Despite its lack of glamor, dubbing requires an unusual skill that many very good actors just don't have. The dubbing actor has to convey the same mood in his speeches as the actor in the film, but without going through any of the motions.Brav, the American director, says he recalls one occasion where a biligual actress was trying to dub her own voice from French into English.

"She had a terrible time; she found it extremely difficult when she wasn't actually acting the role, when she wasn't in costume and didn't have any make-up on."

The most an actor can do to recreate the mood of the film is to make modified gestures himself as he stands there in the recording studio.

Loyer explains: "When the actor in the film reaches down to pick up something, I reach down in the studio. When he eats something, I stuff a biscuit in my mouth."

And when a love scene comes along, "well, you move a little closer physically and you make the necessary sounds," he says, making a kind of smooching sound with his lips against his hand.

"You can go through these kinds of motions, but still you never have quite the same feeling."