Probing the personal and private side of Christopher Lambert, the French fantasy-in-the flesh who sprang out of nowhere to play the lead in Greystoke: The Legend of Tarzan, Lord of the Apes, is proving to be a frustrating business. Not that I expected an easy time of it. Onscreen, Lambert projected a skittish reserve that gave a sweet, sad tone to his portrayal of nature's noble foundling grown into one gorgeous hunk of a man. As Lord John Clayton, a.k.a. Tarzan, in Hugh (Chariots of Fire) Hudson's $30-million version of the Edgar Rice Burroughs classic, Lambert not only managed to look graceful romping around in a loincloth, he was also a knockout dressed to the nines as an Edwardian dandy. So with Christopher Lambert's career off to a dazzling debut, I am in Canada to find out how he looks in person and how he is coping with instant stardom, and to discover the effect success has wrought on his career and relationships. Is that asking so much?

"Nothing in my life has changed," he insists. "I'm exactly the same guy I was before making Greystoke."

Lambert, now 27, seems thinner, paler, more mature than the agile hunter who wrestled panthers and ruled in African rain forests. His face is long, narrow, a thoroughbred. I see in a flash why the camera loves him. If I were a camera, I'd love him, too. He smokes filter-tipped American cigarettes, wears metal-rimmed glasses and is just as handsome as can be.

I have cornered my prey on the top floor of the Monument of National, a disused opera house in a seedy section of downtown Montreal, which is serving as a set for Paroles et Musique, the Canadian-French co-production starring Lambert and Catherine Deneuve that opens this winter (with a different title in the United States).

Deneuve has returned to France, her part done, but Lambert is required in practically every remaining sequence. So between takes we retire not to the seclusion of an air-conditioned trailer, alas, but to two director's chairs arranged on the sidelines of the stadium-sized stage. Slumped in his chair, outfitted in faded, shapeless duds, Lambert looks exactly right for the part he is playing, a young hungry, hippie-inclined Parisian rocker with lots of straight brown hair falling across his face. Yet appearances are deceiving.

"I see the same people. I have the same friends I had before making Greystoke."

"They're in the picture business, too?"

"Oh, no. My friends are the same crowd I've know since school. None of them are actors. They're bankers, real-estate brokers." Lambert, who attended some posh Swiss schools, speaks in a French-accented English that is quite fluent, more American than British. "Of course I don't have as much time for them now as before," he allows.

"Does that go for girlfriends, too? Any special lady?"

"No way. That is utterly impossible." His attention drifts moodily across the field of movie paraphernalia. His blue-grey eyes behind the clear lenses are so deep-set they seem slightly off center with the faintest suggestion of a squint. Sexy. Brooding. Shades of early Warren Beatty.

"I have to be free to go wherever the work takes me," he says finally. "I can't expect a woman to drop everything and follow me around.

"I tried it once, twice," he confesses, "if you count a little bobby-soxer.... But that was long ago. She was really something." He pauses to pay her silent homage. "But this more recent relationship was a real lesson. I met her just as I was beginning my preparation for Greystoke. She's someone with her own career. Yes, an actress. Eight years older than me." He deigns to name names. "I was shuttling back and forth between London and Paris every weekend. It had me on the move. And still, I couldn't give her the attention she deserved. Believe me, by the time she called it quits, Hugh [Hudson] was plenty fed up."

She called it quits? Lambert's ill-fated romance bears a remarked similarity to the scenario of Paroles et Musique, which reads a trifle soapy. The story, in brief, is the archetypical French saga that has the younger man wooed, won and ultimately rejected by an older, wiser femme du monde.

Did that straight-from-life experience feed into Lambert's development of the character he's portraying? Lambert shrugs and reaches for a pack of cigarettes.

"No, yes, maybe...I don't know. I'm not sure. In this movie my character is very restrained - all of his feelings held inside. I like to portray a man pushed to some extreme state... at the edge. When I don't feel it I become afraid I'm just walking through it.

"Anyway," he says, cheering up, "for now the important matter is not so much what I do in French, but that I keep myself busy working, learning, getting all the experience I can. I must be patient and wait till the absolutely right American property comes along. That's one new development," Lambert concedes. "Now the offers come to me. The screen plays pile up on my floor." He holds out his hand waist-high.

"Have any appealed to you?"

"A few. One in particular, which I was told was absolutely wrong," he says with a self-mocking grin. "It was a story about an athlete, but my agent said no way. I'm lucky to have a wise old bird like Sam Cohn."

Lambert takes evident delight in pronouncing the name of his illustrious I.C.M representative. Indeed, it's no small endorsement that a man as powerful as Sam Cohn has decided that Lambert has what the American public wants. It's been ages, of course, since Hollywood had its very own French heartthrob. Who was the last, in the class of Charles Boyer, to make the transatlantic crossover? Louis Jouvet? Not famous enough. Alain Delon? Belemondo? Yves Montand? Not eager, it seems to leave French turf. Gerard Depardieu? Why bother to master English when he already employs the only language worthy of human discourse. Rare is the Frenchman who wouldn't prefer a draft of home-brewed hemlock to the horrors of exile.

"Do you think you could get used to life in America?"

"And why not?" he answers with characteristic Gallic insouciance. "I was born in New York. I still am an American citizen. It's a great advantage as far as taking jobs and dealing with the union. I still have my American passport." He produces the ultimate evidence, then proceeds to clarify the complexities of his dual citizenship.

The actor was born in Manhattan, the younger son of a French diplomat who was attached to the U.N. Besides an older brother, there are three half-sisters from his father's two earlier marriages.

"Your mother is French?" I ask.

"French, Belgian, I can't remember." He brushes aside these banal distinctions.

When Lambert was 2 years old, his father moved the family to Geneva. Like many children of the diplomatic corps, Lambert traveled extensively and attended a precession of boarding schools known to produce highly adaptable habits in the adult species. They're quick studies these adults: They learn new languages, they adopt new customs, and they have a knack for leaving people, places and possessions behind. Lambert was first stagestruck at age 12 in a school play. Yet after receiving his baccalaureate, he went first to London and then to Paris in an effort to please his father, who wanted his son to be a stockbroker. Fortunately, a surfeit of unemployed bankers in both cities killed that scheme. Lambert did his obligatory year's service in the French military and settled in Paris, where he had "a wild time" with the help of a "Parisian nymphet."

Then at age 21, his adolescent resolve to become an actor resurfaced, and he applied to, and was accepted by, one of the more traditional drama schools in Paris, the Conservatoire. "So boring, so dull, all the emphasis on technique," is Lambert's assessment of his formal theatrical training. During the time he was supposed to be attending classes he took small parts in some B gangster movies and had, in fact, been expelled from school when a costume-designer pal introduced him to Hugh Hudson, who was casting Greystoke. And the rest is history.

There followed, eventually, six months of rigorous training, drilling and instruction, a challenge that Lambert seized with all the ardor of a compulsive. He moved to London and began in earnest to learn English, which he scarcely spoke. The other language he was obliged to master was the chimpanzee's screams and signs. He paid a quick visit to the United States to be briefed by a behavioral scientist who specialized in teaching chimps how to communicate. Eventually, at Hudson's behest, Lambert would spend three to four hours every afternoon "chimping" --absorbing the movements and mentality of the simians. "I had to be a chimp, not act like a chimp." When not imprinting apes, Lambert worked on his daily gymnastics routine, the rings and parallel bars, to develop the necessary strength and agility to fly through the air and shinny up tree trunks. All of it, of course, was only preparation for the hellish main bout in equatorial West Africa, where the heat clocked in at a sizzling 120 degrees. Lambert recounts it all as a great adventure, though not an easy act to follow. Now his biggest problem is that his present role isn't sufficiently demanding--it doesn't push his "limits."

In the midst of Lambert's lament, and overwrought Canadian with round, apologetic eyes of materialize and breaks into an agitated stream of French.

"They need me to rehearse the next scene," Lambert reports, and we arrange to meet up the following day at noon, on the tennis courts near his hotel, where Lambert invariably begins his day. It's hard to believe he will make it. He expects they'll be shooting till 3:00 or 4:00 A.M. In addition, seen under the bright lights, Lambert is not a particularly hearty sight. He looks ashen, ill, his expression melancholy.

"Hey, you better get some rest," I urge him. Lambert, it seems, has a vulnerable quality that brings out the maternal in otherwise sensible women.

"I'm fine," he protests. "As soon as I start to work, the energy is there. All my pains and aches disappear."

But indeed, mother knew whereof she spoke. Our courtside appointment is canceled because, as a bellhop later informs me with a satisfied leer, "Tarzan ees seeck wiz ze flu."

I next catch up with my man in New York at his suite in the Sherry-Netherland, where the desk clerk instructs me, "Mr. Lambert is on a Paris call, but he says go right up. The door is open." I am here on a quiet Sunday morning to drive out to Kennedy with him. He arrived in New York the day before and is booked on a flight to Tokyo for his premiere of Greystoke.

The elevator is empty. The sitting room of his ninth-floor room is empty. I can hear him on the phone in the adjoining room, so I settle into a corner of the ivory-colored couch. This room looks undisturbed, unlived-in, except for a tray on a table with the remains of a tea served for one. There is an unopened bottle of wine, compliments of the management. The stillness is quite a contrast to the commotion surrounding our previous meeting. No crew hanging around, no entourage. Lambert comes into the room, immaculate, smoking away, apparently in great spirits. "Hi," he says, and immediately there is another call, this one from the hotel announcing the arrival of his car. Except for the familiar aviator glasses, Lambert is a brand-new man, pressed polished, dressed in blending shades of beige, his hair slicked back, neither English lord nor Parisian hippie. Not bad, not bad at all. Whatever bug caught him in Montreal is gone.

Another call. Paris again. He is visibly more relaxed yet charged with energy. The only sign of departure jitters is the chain smoking. Before we leave the suite I hand him a weird little stickpin in the shape of a chimpanzee I'd bought from a street peddler. He pins it to his jacket and reciprocates with the bottle of wine. "Please," he urges with impeccable French logic, "if you don't take it, it will go to waste."

"We've decided on my next picture," he tells me as soon as we are comfortable seated in the limousine, a transit undisturbed by paparazzi or fans. "I'll be playing in it with Isabelle Adjani. It should be finished by the end of October, beginning on November, and by then we may find the right part in America...." His attention drifts off as he inspects the city streets outside the tinted windows. The place where he was born. Does it stir up early memories?

"Did you ever dream when you were growing that you'd be traveling this way all over the world?"

"I did travel all over the world when I was growing up," he reminds me. "Dreams," he continues, "dreams are nothing. Okay, sometimes you have a private dream. I'll give you an example. The first time I was in London, I was walking along a beautiful street lined with beautiful old houses. Mount Street. Do you know it? And I thought, one day I will live here. And when I went to London for my Greystoke training, where do you think they had arranged for me to live? On Mount Street. They're very pleasant, these accidents. But they don't change who you are. You remain the same person. I don't speak of poverty. Of not having enough. That's another matter. To live in misery... awful. But these dreams you refer to..."

I can hear the diplomat's son speaking, the boy taken by his parents to strange places and underdeveloped nations. Another school, a new set of rules, constant change.

"What about fame? Being recognized? Fans clamoring to meet you? Would that be another Mount Street?"

"If fame comes before you're ready, it can be a disaster. So many guys have lost it all that way. Burnt out. Luckily, I have plenty of time to find out who I am.

"Wherever I am," he says as though to sum it all up, "I'll continue to be myself. And the more mature, the more secure I become, the better prepared I'll be for what comes next. For me the only danger is to be satisfied with what I have, to be stuck protecting an image of myself. I like to be amazed." He laughs, and adds, "I'm too influenced by comic books perhaps."

"Such as Tarzan?" I venture.

"Oh, no," Christopher protests, "Tarzan is much too realistic." He stares out the tinted windows of the limo at the tangle of exits and entrances feeding onto the Long Island Expressway. "New York, this town," he says with a private smile, "is more suited to my taste."