MARTINA. By Martina Navratilova with George Vecsey. Knopf. 287 pages. $16.95.

THE FIRST TIME I saw Martina Navratilova, she was an overweight, seemingly awkward 16- year-old with cropped brown hair, no waistline, and a hamburger in her hand. Ill at ease speaking English, she pointed to the motto on her tee shirt and said, with a heavy accent, "I can't believe I ate the whole thing."

It has always been hard for me to reconcile that first impression with today's sleek, glamorous, blond, colloquial, vegetarian Martina, who has dominated women's tennis for the past three years. Her autobiography, ably crafted by New York Times columnist George Vecsey, goes a long way toward illuminating how her remarkable transformation took place.

This is no ordinary celebrity profile. As Martina herself points out, she has long been labeled the "bisexual defector." Those two words alone suggest why her climb to the top is so singular. In a sport where players are quite shielded from the press, Martina often has been on the spot.

Here she responds with extraordinary candor, a trait not usually found among her colleagues, while displaying a fine intelligence, too. Not that there are any X-rated passages. You don't have to hide the book from your teenaged daughters. Still, she is the first female sports megastar to step proudly out of the closet, waving Old Glory to boot. "Being blunt with your feelings," she declares, "is very American."

Now 28 years old, Martina grew up as a tomboy in Czechoslovakia, a country in which, according to her, there was no stigma attached to athletic girls. Among her earliest memories is the exhilaration of her first sport, skiing (her mother was an instructor). Other memories center on living in a single room overlooking a ruined tennis court, on what was her mother's family's estate before Communist rule. When she was 12, she witnessed the bloom of the 1968 Prague Spring fade into the drab horror of the Russian invasion. Her childhood coach, George Parma, was out of the country and never returned. For Martina Navratilova, politics and tennis were inescapably intertwined.

Her personal life was unconventional long before she reached the United States. Her parents were divorced when she was very young. Only years later did her second father (so close is she to him that she refuses to call him her stepfather) tell her that her natural father had committed suicide some years after the divorce.

She was a late bloomer; Parma initially thought she was a boy. She was late reaching maturity on the court as well; when she first began playing on the international circuit, Chris Evert, two years older, was already a fully developed champion. In fact Chris was so well known that she was Martina's grandmother's favorite player!

The detailed account in Martina of her Czechoslovakian years sets the stage nicely for the teenager's arrival in the United States, and makes it clear why she was destined to make it her home. "I didn't feel I belonged anywhere, until I came to America. . . . I honestly believe I was born to be American. With all due repect to my homeland, things never really felt right until the day I got off the plane in Florida. . . . I was able to see America without the filter of a Communist education, Communist propaganda. And it felt right," she writes.

IN ADDITION to her highly publicized romance with junk food, Martina fell in love with American material goods, American free speech, American sexual openness. It is not surprising that she wound up with a car for every day of the week, houses of every description and female lovers in each of them. What is surprising is that she tells us about it all.

Okay, maybe not all. You won't find any new names here. But her autobiography sure picks up speed once she gets to the moment in 1975 when she decided to defect, right in the middle of the U.S. Open at Forest Hills.

In retrospect, it's amazing that the bloated, emotional teenager ever got a chance to become the dominant player in the world, considering that she had to become a grownup, find new friends, learn a new language, all in the context of the globetrotting gypsy life of the pro tennis tour.

How did she do it? She had the knack (or the smarts) for picking friends and lovers who provided key support at crucial times. A casual meeting led to her alliance with Sandra Haynie, the golfer, who introduced Martina to Dallas, her eventual home, and who took control of her diet and her finances. Then came people like Rita Mae Brown, the novelist, for whom she displays a great deal of residual affection, who showed Martina there was a life beyond the courts. Her relationships with Nancy Lieberman, the basketball player who taught Martina the value of hard training and who drilled motivation into her, with Renee Richards and later Mike Estep, her coaches, and with Robert Haas, who disciplined her appetite, are well chronicled here, although we must keep in mind that we are only hearing Martina's side of each.

For me, her most fascinating relationship, still very much in evidence, is with Chris Evert Lloyd. On the one side we have a good Catholic All-American heterosexual, a national sweetheart at 16, a baseliner. On the other side: the Bisexual Defector, an impetuous server and volleyer, whose entourages -- Lesbian novelist with a cat named Baby Jesus, Jewish female hoopster turned born-again Christian, transsexual coach -- sound like inhabitants of John Irving Country.

Chris vs. Martina grew into the most intense rivalry for female tennis supremacy since Lenglen and Wills; yet in the process, they became good friends. Martina describes, in fact, how Lieberman tried to drive a wedge between her and Chris . . . and failed. Somehow I can't see male rivals sharing a bagel in the locker room at the 1984 U.S. Open, then going out and blasting away at each in one of the most searing final matches on record. Martina should be grateful to Chris and vice versa; they have made one another tougher champions.

There is very little in Martina about the tangled web of the business side of tennis, thank goodness. And her descriptions of key matches are surprisingly stilted. She admits that she is not an introspective person. But she sure is an honest one. When her father, whom she describes as holding "a macho, fifty-years-behind-the times Czech view," discovered she was living with a woman, he unloaded every homophobic clich,e, ending with "there must be something wrong with you physically."

Martina replied, "Everything's in working order." Anyone who has seen this sensational athlete in action will agree wholeheartedly.