Sir Alec Guinness, slippery chameleon of the screen, flops his legs over the side of an armchair in a strikingly boyish way. He is 69 years old, and here, in his suite at the Connaught Hotel, his conversation is animated and good-humored. He has the manner and presence of a private man, but not a timid one.

"With hindsight," he says, "I know I've been an actor since the age of 4. I can't imagine being anything else. In fact, I've been very lucky. I don't know whether I'd like to be an unlucky actor . . .

"I just enjoy acting, finding a different personality. I think I had a lonely . . . well, I jolly well know I did, I had a lonely childhood, apart from school days. And I've always maintained that actors are kind of undeveloped adolescents for the most part. They've gotten stuck emotionally and spiritually at 15 or 16. So I'm not seeking fame, or indeed, money particularly. I would just love to give one performance that I could go out thinking, 'Well, they could never discredit that!' "

His self-effacing modesty is appealing and has the ring of sincerity, yet with an actor as good as Guinness, how can you really tell?

Valentino was the greatest of screen romantic heroes. John Wayne was the quintessential Hollywood cowboy; Marilyn Monroe, the most enduring sex symbol. Alec Guinness, nearly 50 years into his career and still in top form, is earning a similarly unique place in film history. He is the ultimate character actor.

Comedy to tragedy, leading man to walk-on, the range of his portrayals in movies and on the stage is vast: Hamlet, Richard II and III, Fagin, Disraeli, Pope Innocent III, eight different parts in "Kind Hearts and Coronets," Col. Nicholson in "Bridge on the River Kwai" (for which he won an Oscar), Marcus Aurelius, the mysterious Yefgraf in "Doctor Zhivago," Hitler, Obi-Wan Kenobi in "Star Wars," Smiley, John le Carre''s enigmatic spy and, most recently, Freud in Marshall Brickman's romantic comedy "Lovesick"--to name just a handful.

Acting genius is not merely enormous talent. It involves a whole persona. Alec Guinness' special quality is that he keeps his almost completely submerged.

"He is a master," the late critic Kenneth Tynan wrote of Guinness in 1953, "a master of anonymity . . . The whole presence of the man is guarded and evasive. Slippery sums him up; when you think you have him, eel-like he eludes your grasp . . . Were he to commit a murder, I have no doubt the number of false arrests following the circulation of his description would break all records."

Even a dedicated filmgoer and Guinness fan is unlikely to know much about him. There is no firm public image, no controversy; just scores of brilliant portraits that tell next to nothing of him, but a great deal about the character he is playing. He has been married to the same woman for 45 years, and they lead a retiring life on 10 acres in the Hampshire countryside. He abhors parties. Because his own persona never gets in the way, Guinness seems able to be pretty much whatever he chooses.

He doesn't seek out interviews, but once he's agreed to do one, Guinness tries his best to make the reporter feel at ease. He chooses late afternoon, after a day of dubbing sound for "Return of the Jedi," the next "Star Wars" epic, and answers the door with a friendly greeting that is more than polite and less than hail-fellow-well-met. He is wearing a green cashmere sweater, glen plaid trousers and slippers. He offers a drink but takes only mineral water himself, and he smokes Dunhills one after the other. Although he's reticent about money matters, he converses easily about his encounters with other stars--most notably Grace Kelly and Sophia Loren--his view of his craft, his conversion to Catholicism, his favorite roles and how he became an actor in the first place.

"I gave my best performance, perhaps, during the war," he relates, describing his ascent in 1941 from ordinary seaman to commander of a small supply ship. "I mean, pretending to be an officer and gentleman. You had to act your way through it, pretending you knew where you were going and what you were doing . . . When I went up for my commission, I was obviously nervous. A very good friend of mine said, 'For God's sake it's a part, act it.' And that's what I did."

ALTHOUGH he stays far from the glitz and glamor of Hollywood, Guinness is generally tolerant of his colleagues in the field. "Funnily enough, actors are less bitter, less bitchy than musicians and writers, who are terrible about each other. I think we're a desperate brotherhood in some way."

One of the few Guinness stories that is already part of Hollywood lore concerns a souvenir tomahawk that he and Grace Kelly volleyed back forth for about 25 years, almost to the time of her death in an auto accident last fall.

The exchange began when they were filming "The Swan" (1956) in North Carolina, Guinness recalls, with Kelly presenting the tomahawk to him as a present: "I didn't want to carry a bloody great tomahawk around with me and as I left the hotel, I gave a dollar or something, which was quite rich in those days, to the hotel porter and said, 'Put that in Miss Grace Kelly's bed . . .'

"Years pass, Grace becomes the princess of Monaco and all that. One night I get home in the country, a summer night. I get into bed and say to my wife, 'Why the hell is there a cold hot water bottle in this bed?' It was the tomahawk! She knew nothing about it, but Grace had got into my house . . ."

Back and forth it went. The tomahawk even turned up in a bed in the Beverly Wilshire Hotel in Los Angeles when Guinness was there for the Oscars. Then, some time in the past the year or so, Guinness had it stuffed under a quilt in Kelly's hotel bedroom. Somehow she missed it, he says, but a co-conspirator "saw her attache' case with lingerie and odds and ends and quickly put it in there. When she locked it and went to pick it up she thought 'this has suddenly become heavy.' And then the scream came. And that was the end of it, alas."

But his memories of Kelly are more complicated than just a long-running gag: "She was a strange girl, I liked her very much. But I think she could only give her attention to one person at a time. I don't mean this in a sexual or romantic way. I was a strange new arrival when we did 'The Swan' in 1956 , so for the first month I was feted and wined and dined. We used to go for walks together, laugh together and she was very easy, very nice. Then someone else arrived and I was rather . . .

"It was a little like that, it was a little bit like trying to show who's in charge here or the boss. I don't mean it in an unkind way. I've known other people like that. She was a very nice girl, a nice, sweet woman. It's very sad that she's gone."

Guinness' recollections of Sophia Loren have a similarly avuncular quality of platonic intimacy. Once in Madrid, he remembers, "I asked her out to dinner a deux. I went to collect her. It was a night of horrible rain, mud and slosh. She came down the stairs of the apartment in a wonderful white evening gown. She was rather over-glamorized for where we were going.

"The car was outside and she slipped on the muddy wet pavement and went slap on her face, ruining the dress. She also grazed and bruised her face. I was very upset and whipped her inside saying, 'Well, we'll cancel it and make it another night.' 'No, no, no,' she said, 'give me 10 minutes.' And up she went, cleaned herself up and got into another dress as if nothing had happened. There was thousands of dollars of ruined silk and her face grazed.

"I thought she was marvelous . . ."

GUINNESS thinks long and hard about the characters he depicts and has always said that in copying from real life, it is essential to get the walk right. But sweepingly emotive mannerisms are not his style either. He calls himself "a miniaturist" whose portraits more often than not are helped by the close-up lens of a movie camera.

George Smiley, which Guinness did in two separate six-part series--"Tinker, Tailor, Soldier, Spy" and "Smiley's People"--for television over the past three years, is probably his favorite. It's easy to see why.

His best roles, Kenneth Tynan wrote, are "iceberg characters, nine-tenths concealed, whose fascination lies not in how they look, but in how their minds work, people with secrets to hide from their fellow men . . . his territory is the man within." John le Carre', author of the Smiley books, says the reason Guinness works so well with his material is that, "We both have an obsession with mannerism and character."

Guinness' explanation: "I always hope that I've only got to think something, and somehow some chemical reaction with the audience will put over what I'm thinking. Take Smiley, for instance. In questioning a person, his face has to be blank or else the intention is given away. Therefore the acting has to be strongly interior, to have a double, to ask the question, but to have another thought behind it."

Guinness says he especially enjoyed the sustained intensity of spending so much time in the character, 12 hours in all. And although he plans to do one more short play as Smiley (delivering a soliloquy on the intelligence business to eager spies-in-training), he says he would not do another full-scale television production in the role. "I've carried stillness and nonreaction as far as I can go," he says. "I've got to pedal on furiously to something else."

His determined quest for the next challenge, with the implied feeling that somehow he might not be able to meet it, a refusal to be blase', these may well be the keys to Guinness' lasting strengths. Given a chance to start over, would he do the same? "Oh yes," he says chuckling, "I'd just pray that I would have the good fortune I've had. I've been almost ominously lucky."

TALKING ABOUT prayer is not just a figure of speech to Guinness. He and his wife converted to Catholicism 25 years ago and are regulars at their local parish. He was born an Anglican, but he was, he says, "anticlerical, certainly agnostic if not atheistic."

But then something began to draw him to the church: "I don't know what it was, I suppose a sense of worship, something outside oneself, possibly."

The moment of his conversion came, characteristically, when he was playing a part:

"One day I was filming in the middle of France and was dressed, absolutely inaccurately I now know, as a priest. We were filming at night, location stuff. It was a little mountaintop village and I had a room to change somewhere else, a mile and a half away. They said they'd need me at 10 p.m. but when I got there, they said it would be more like 2 a.m.

"So I turned and started to walk away. It was getting dark and suddenly I heard footsteps behind me. There I was in this cassock and it was a small boy, age 7 or 8, and he pattered along. He must have seen I was not a familiar figure. I mean, I wasn't his local priest. But he took my hand and held my hand all the way down, prattling away. I didn't dare answer him in case my appalling French frightened him.

"Suddenly, with a 'Bonsoir, mon pere,' he disappeared into a hedge. Sweet little kid. And I thought, my God . . . I changed my attitude at that very moment because, I thought, a religion which can provide whoever is wearing that particular robe with an air of comforting security so that a kid in the night knows that he's a perfectly safe person to run up and take his hand to prattle with, has got more to it than I had credited it."

Among his many friends in life, Guinness has several whom he feels are directly connected to his Catholicism, "a priest here and a priest there," the writers Graham Greene and the late Evelyn Waugh. There is, he says, a "bond."

WHEN NOT actually filming, Guinness comes to London only about once a week and stays in a small suite at the Connaught, a bastion of understated British luxury. Running up substantial hotel bills is possible now, Guinness says, because his agent persuaded him to take a small share of "Star Wars" profits in lieu of a fee.

He calls the take a "nice lump" but won't hint how big. "I don't like talking about finance," he says. "Like all actors except those who made a Hollywood career or those who salted it away before taxes got so high, I've never had much. Oh, I've made lots of money, but no one's been able to keep it in this country."

He could have made lucrative commercials, it is pointed out. After all, Lawrence Olivier plugs Polaroids. John Houseman peddled Chryslers. David Niven did coffee.

"I was passing a bus queue once," Guinness recalls, "and a bus drew up and on the back of the bus there was a poster advertising cigarettes with a picture of my old friend Jack Hawkins. I heard two old women say, 'Oh I'm so sick of that face on the back of a bus.' And I thought, ah, ah, ah . . . no, I don't want to see myself on the back of a bus. It would make me wince every time, or cropping up on the box. I would love the cash. I've toyed once or twice with good offers. What the hell, why not? But then I decided, if I can manage without, I will."

When it comes to politics, Guinness keeps a predictably low profile, while harboring strongly held but coolly expressed beliefs. By instinct he feels closest to Britain's center parties, the new Liberal-Social Democratic alliance, which pursues nondoctrinaire economic and defense policies that appeal to his sense of moderation. His strongest feelings are about the dangers of nuclear war.

"From 1945 we have lived with this horrendous possibility hanging over us," he says. "We live in a world of fear and somehow that has got to be tackled." But he is definitely not a man for the barricades: "I so dislike actors and people who make their name in another field sounding off as individuals in some party way . . ."

As he begins his 70th year Guinness is reflecting on his past and writing a book of reminiscences about those who influenced him most. He is two-thirds of the way through a draft, writing by hand and then typing the manuscript, making changes as he goes along: "Being an amateur writer, it means I have to be in the mood to do it, whereas my own job I have to do whether I'm in the mood or not."

The book will feature the actresses Martita Hunt and Dame Edith Evans, with whom he worked in the early days, and the director Tyrone Guthrie, who gave him his first lead in a modern-dress Hamlet at the Old Vic in 1938. But his greatest admiration is for John Gielgud, now 79, who spotted Guinness in a drama-school competition in 1934 and started giving him parts.

"Practically everything that's best in the British theater has stemmed from Gielgud," Guinness asserts. "He was the first to start employing foreign directors and foreign designers. He made us less parochial, not intending to, I think, but just by his inner good taste. And he was a great romantic actor.

"I was tremendously lucky working for Gielgud, a disciplinarian who stiffened one up. Guthrie was exactly the opposite. He was wonderful at encouraging the young . . . You could try anything." AA S THE interview stretches into the evening, Guinness remains A engaged and gracious. There is no surreptitious glance at a watch, no telephone call to disturb his privacy. Alec Guinness is a gentleman, too genial to be awesome, too self-contained to be truly open.

Last month, when he received a British film and television academy "Oscar" for his portrayal of Smiley, Guinness stepped to the podium, his head a little bent forward, and accepted the award. He spoke not a single gushing word. That he was present at all apparently was evidence enough of his respect for the prize and gratitude that he had won it.