AT HIS BIRTH on February 20, 1927 in Miami, Florida, Sidney Poitier weighed less than three pounds. He was so frail and sickly, in fact, that his father, Reginald, a poor tomato farmer, began building a tiny coffin. Only his mother, Evelyn, believed he'd survive, and she nursed him day and night. Finally, when he grew no better and everyone in the family said he'd die, she went to a fortuneteller for comfort and advice.

The fortuneteller, after much eye-rolling, glared into a cup of soggy tea leaves and predicted: "Don't worry about your son, he will survive . . . He will grow up to be . . . rich and famous. Your name will be carried all over the world."

With that Evelyn hurried home and had her husband throw away the little coffin.

Today Sidney Poitier is indeed rich and famous, a social symbol of a sort. Celebrated as the first black actor to break through the sterotyping and racism of Hollywood, he has individualized and humanized the black experience with powerful performances -- among them, the rebellious student in Blackboard Jungle, the anguished chauffer in Raisin in the Sun and the footloose handyman in Lilies of the Field, for which he won the Academy Award.

Now he's written his autobography, which is an energetic in style and as decent as his on-screen image. Throughout the book he underplays his achievements and reveals the genuine responsibility he feels for his race. Mainly, though, he concentrates on telling the rich, painful, exhilarating story of his life, an epic personal struggle.

From three months of age until he was 11, Poitier lived with his family on Cat Island in the Bahamas. Then they moved to Nassau, where home was a stone hut with a thatched roof. The youngest of seven children, Poitier spent his days roaming the island, playing with turtles, catching fish, swimming. He attended school for only a year and a half.

He had never heard of racial prejudice until at age 15 he was sent to Miami, where he saw "white" and "colored" signs everywhere and people ridiculed his West Inidan accent. For a while he worked as a delivery boy; once, lost in a white neighborhood, he was dragged into a car occupied by four policemen who held a pistol to his forehead and joked as to whether they shwould shoot him in the right eye or the left.

In 1941 he left Miami on a freight train, wanting only to go north. He got as far as north Florida, where a policeman called his brother, who took him back h ome. But before long he was gone again, and eventually, nearly broke, he reached New York by bus. He got a job washing dishes and , until he had saved some money, slept on the roof of the Brill Building stretched out on copies of The Times or the Journal-American. When the cold weather came, he was so miserable that he decided to join the Army to get away from it, but he was assigned to duty on Long Island. After a little more than a year in the service, he returned to New York, where he was a truck driver, elevator operator and dishwasher in restaurants all over the city.

In 1944, he auditioned for the American Negro Theatre, where he was brusquely told he had a terrible accent and "You can't be an actor and not be able to read." These remarks enraged Poitier. He decided then and there that he didn't want to be a dishwasher for the rest of his life. "First and foremost," he resolved, "I have got to prove . . . that I can become an actor."

He bought a cheap radio and spent his free time listening to news, commercials and song lyrics in an effort to rid himself of his accent. During breaks on his dishwashing job an elderly Jewish waiter helped him polish his reading and pronunciation. "I would come out of the kitchen and sit down next to him and read articles from the front page of the Journal-American. When I ran into a word I didn't know (and I didn't know half of the article, because anything past a couple of syllables and I was in trouble) he explained the meaning of the word and gave me the pronunciation and then sent me back to the head of the sentence so I could grasp the word in context." He was wonderful, and a little bit of him is in everything I do."

By 1946 Poitier was accepted at the American Negro Theare and started taking classes and acting in projects. Later he understudied in the road company of Anna Lucasta, remaining with the show until 1949, playing a variety of roles including the male lead.

Then in 1950 Joseph Mankiewicz chose him for his movie No Way Out and recommended him for the part of the heroic young priest in Zoltan Korda's production of Cry, the Beloved Country. Poitier tells a terrifying story about the making of that movie. He was almost murdered by a carload of white thugs during a wild car chase on his way out of Johannesburg.

There are many other incidents of high drama -- the book is filled with anecdotes and portraits -- of Poitier's tempestous romance with Diahann Carroll, of his two marriages, his six children (all girls), his friendship with Harry Belafonte; there's also a section devoted to his lenthy analysis.

Subsequent chapters revolve around the politically volatile 1960s,, when Poitier was starring in some of his most successful movies like Guess Who's Coming to Dinner? but he was being regularly attacked in print for playing only "bleached-out roles."

In his own defense Poitier maintains: "Hollywood . . . wasn't interested in supplying blacks with a variety of positive images . . . The closest Hollywood came . . . was the one-dimensional middle-class imagery I embodied most of the time." He adds, "I also understood the value system of a make-believe town that was at its heart a racist place."

But by portraying a teacher in To Sir With Love, a homicide detective in In the Heat of the Night and a psychiatrist in A Slender Thread, he believes he's made progress for other black actors.

Now Poitier spends much of his time directing box-office hits like Uptown Saturday Night. Recently Ebony magazine listed him as one of the two top moneymaking black directors in Hollywood (the other is Michael Schultz). Poitier says he hopes his future movies will delight blacks and intrigue whites -- he has never had any interest in "putting whitey down."

Clearly the intention was the same in his large-spirited, informative autobiography, one of the best additions to the small library of books on the black artist in films.