BLESSINGS IN DISGUISE. By Alec Guinness. Knopf. 238 pp. $17.95.

THROUGHOUT HIS LONG, various and exceptionally distinguished career, Sir Alec Guinness has been an actor who absorbs himself into the characters he plays rather than one who attempts to impose himself upon them. Guinness the actor is well known to us, but Guinness the man is not; whether by design or by nature he has chosen to keep his distance from his public, remaining something of a mystery himself even as we feel an intimate knowledge of the astonishingly diverse characters he has created. Thus it is no great surprise that the Guinness who emerges in his own memoir -- a book he describes as "not so much a patchwork quilt of memoirs as a cat's cradle of reminiscences, all tangled round myself" -- is modest and self-effacing. He warns at the outset, speaking in the voce that he calls "Ego":

"He is not at all proud of himself or his achievements and is equally attracted and repelled by the limelight, as if never quite sure how to present himself, or who he is or what he would really like to be. Deep in his heart he hankers to be an artist of some sort, but he is only an actor. To be an actor was his adolescent dream and has been his means of livelihood for fifty years or more; but although he has no complaints about that (indeed it would be ungrateful of him to make any) he knows that an actor is usually no more than an assortment of odds and ends which barely add up to a whole man. An actor is an interpreter of other men's words, often a soul which wishes to reveal itself to the world but dare not, a craftsman, a bag of tricks, a vanity bag, a cool observer of mankind, a child, and at his best a kind of unfrocked priest who, for an hour or two, can call on heaven and hell to mesmerize a group of innocents."

One need only read that passage to understand that beneath the modesty is a crafty and self-aware man who has consciously sought to keep Ego under control so as to put it in its place. He is fully aware that Ego has much to do with his desire, or that of anyone else, to spend a lifetime on stage; he also realizes -- as, in this age of television and film, fewer and fewer actors do -- that the role is what matters, not the person who plays it. Consistent with that view, he has chosen to offer us relatively little of himself in Blessings in Disguise, preferring instead to write about those men and women whose influence on his life was large and beneficent. Even here he keeps his distance, telling much about theatrical people with whom he has been close but relatively little about his immediate family. On only one matter of genuine intimacy, his conversion to Catholicism, can he be said to open his heart to the reader; otherwise he does an impressive job of staying in the background in his own autobiography.

This may seem at first glance a shortcoming, but it proves to be quite to the contrary. For one thing, the men and women about whom he writes are giants of the 20th-century stage: Tyrone Guthrie, John Gielgud, Ralph Richardson, Sybil Thorndike, Edith Evans. For another, he writes about them with such wit, candor and affection that he proves as splendidly gifted at creating characters on paper as he is on film. Though some readers will be frustrated that he offers little backstage gossip about the specific plays and films in which he has appeared, most are likely to agree that this is more than offset by the charm of the portraits he paints.

If there is a common thread through all of them, apart from the theater, it is kindness. Though he is never saccharine about it, Guinness has been received generously and sympathetically since, as a 16-year-old schoolboy in 1930, he wrote a note to Sybil Thorndike asking how the thunder and lightning had been done in her provincial production of The Squall; she wrote right back, invited him to appear at the stage door, and with her husband Louis Casson gave him an energetic demonstration of the special effects. What Guinness does not say, though it is easy enough for us to conclude, is that he was a bold and determined young man to write a note to so formidable a figure, and that Thorndike must have found him a most appealing fellow to welcome him as she did.

SO DID MANY others, though their kindness sometimes took peculiar forms. Seven years later Guinness played the title role in a production of Richard II directed by Ralph Richardson: "His only piece of advice to me, before we went into rehearsal, was to hold up a beautifully-sharpened Venus pencil and say, 'Play it like this pencil, old cock.' I wasn't greatly illuminated." A meeting with George Bernard Shaw was nothing if not memorable: "I was standing nearest to the door and nearly caught the old gentleman as he hurtled into the room in his purple woollen suit and green knitted tie. He was unexpectedly tall and rather beautiful; his fluffy blanco-white beard and pale baby-smooth skin were particularly striking. He entered smiling and full of greeting, with a hand extended to be shaken, but I hadn't been told how poor his sight was: I put out my hand to take his and he missed me by a yard, scampering past but calling out joyously, 'I have just put the finishing touches to the play.' 'Oh, well done!' cried Mrs. Shaw, clapping her hands."

Of no one does he write with greater affection than Edith Evans and John Gielgud. The former he considers "the greatest high- comedienne and probably the finest actress in the English-speaking world," though he has no illusions about her occasional lapses into meanness and egocentricity; what he remembers her for is the incredible generosity she showed him, especially at one low point in his early career when she went out of her way to demonstrate her confidence in his abilities. As for Gielgud, when Guinness met him in 1934 he quickly became "my actor-hero, benefactor, patron and later good friend, who gave me my first proper chance in the theater, cherished my barely visible talent and kept me solidly employed for two years."

The talent that Gielgud spotted matured more quickly than Guinness admits, shaped not merely by the influence of others but also by Guinness' innate ability to absorb into himself the "habits, idiosyncrasies and personalities" of others, characteristics he was able to use in a multiplicity of roles. It is revealing that he prefers Buster Keaton and Stan Laurel to Charlie Chaplin, Edith Wharton to Henry James; the artist who calls attention to himself is not for him. He writes: "Alan Bennett said to me not long ago, 'I hate Great Acting' -- and I knew what he meant: the self-importance, the authoritative central stage position, the meaningless pregnant pause, the beautiful gesture which is quite out of character, the vocal pyrotechnics, the suppression of fellow actors into dummies who just feed, and the jealousy of areas where the light is brightest, and above all the whiff of, 'You have come to see me act, not to watch a play.'"

There is none of that in Guinness' own acting, and there is none of it in Blessings in Disguise. Whether he is describing his acting or his wartime service, his religious conversion or his attempt to learn the identity of his father, Guinness never once stoops to the theatrical. He prefers to be "down-stage, very much to the side, and with his back half- turned to the audience," and this he is for much of his own memoir. Yet the man emerges all the same: a good man, respectful and considerate of others, utterly serious about his life's work, committed to the highest standards both professional and personal. And, into the bargain, a most beguiling storyteller.