ALL IN A LIFETIME An Autobiography By Dr. Ruth Westheimer with Ben Yagoda Warner. 225 pp. $17.95

Ruth Westheimer -- "Dr. Ruth" to thee and me and all the ships at sea -- is nothing if not an American phenomenon. Three decades ago she came to the United States from Europe with little more than the proverbial clothes on her back, with no knowledge of English and no likely prospects; now her pixie's face and thick German accent are known coast to coast, her counsel about sexual behavior is followed by millions, and she is motored by limousine to her first-class airplane seats. As she says: "Let me say it one more time -- what a country."

And what a lady. Forget the commercials for condoms and soda pop and chocolate mousse and all the other ways Dr. Ruth has cashed in on her celebrity; for that matter, forget the sex chat that is the source of her e'clat. Concentrate instead on the woman herself, the person whose life's story is told in this engaging if artless book, and what you have is further testimony to the human capacity for survival, growth and transformation. It doesn't happen often these days, but with Dr. Ruth it is true: Behind the veneer of celebrity is a real person.

More than that, a real person whose life has included its full share of suffering and sorrow. Born nearly six decades ago in Frankfurt with the name of Karola Siegel, Dr. Ruth left that city in January of 1939 under most unhappy circumstances: Her parents were sending their only child to a children's home in Switzerland that had agreed to house Jewish youths from Germany. Karola Siegel was one of 100 from Frankfurt who had been chosen. When she said farewell to her mother and grandmother at the railroad station, it was for the last time; she never saw them, or her father, again, and to this day she does not know how or in what form they met their fate.

She was in Switzerland for six years; she missed her family dreadfully but refused to grieve openly. At war's end she emigrated to Palestine, where she worked in a kibbutz, trained to become a kindergarten teacher, had a happy sexual initiation and was severely wounded in the fighting that broke out after Israel gained its independence. Her first marriage ended in divorce in France, where she was studying at the Institute of Psychology at the Sorbonne; her second ended similarly a few years later in New York, not long after the birth of the first of her two children.

It was in 1961 that she met Manfred Westheimer, chief engineer with a consulting firm, to whom she has been married for a quarter-century. It was also at this period that she began to develop a career for herself, first in sex education and then as a sex therapist. She got her PhD at Columbia's Teachers College in 1970 -- "it was the closest thing to heaven I ever experienced; I didn't ever want to take that gown off" -- and after teaching for about a decade found herself offered the chance to do a weekly, late-night radio program discussing sexual matters. The rest is history, or at least popular history.

The career upon which that radio show launched Dr. Ruth has taken her from the Johnny Carson and David Letterman shows to college campuses and lecture halls overseas. Precisely why she has been such a success at it is still something of a mystery, but there are some plausible explanations. As she is herself well aware, she is rather a figure of fun; her diminutive stature (she is 4 feet 7 inches) and distinctive accent provoke affectionate laughter, as do her outspoken opinions. Her willingness to talk candidly and amusingly about sex is obviously also important; she addresses herself to a subject for which our curiosity matches our appetite.

The most important explanation, though, seems to be that Dr. Ruth comes to us utterly real, wholly devoid of pretense or sham. She likes other people and unabashedly shows her feelings; she respects other people's privacy and refuses to make sport of their sexual confusion or inadequacy; she takes her listeners seriously, but not herself; and above all, she brings common sense and compassion to a subject too often clouded by hyperbole and exploitation.

Dr. Ruth's long professional training and advanced degree are all well and good, but they are relatively unimportant to her success and the wide respect with which she is regarded. Sexology, like psychology, is little more than mumbo jumbo unless the person who practices it is free of cant and self-preoccupation; Dr. Ruth is precisely such a person, which is why so many listeners are willing to overlook her stature and her accent and to listen, instead, to her wise heart.