Myrna Loy On Screen and Off : MYRNA LOY Being and Becoming<i> by James Kotsilibas-Davis and Myrna Loy (Alfred A. Knopf: $22.95; 358 pp., illustrated) </i>

If you’re looking for one of those gossipy, nasty Hollywood memoirs, written by aging stars who are out to settle scores, Myrna Loy’s “Being and Becoming” is not for you.

The chronological narrative--starting on her Aug. 5, 1905 birthday in Helena, Mont.--is effectively studded with remarks from people who were involved in her life--just one at a time and generally relevant to an event Loy has just finished describing.

Surprising as it may be to some of her fans, Myrna Loy has played more than a sophisticated Nora to William Powell’s Nick in the 14 unforgettable “Thin Man” films--although her celebrity is immortalized by those films. She’s more than a witty redhead with a saucy nose who married four times and never regretted a one of them--”Each of my husbands brought me so much life, so many aspects of the world that might have eluded me.” Of her philandering husband Gene Markey (he was No. 3), she merely says, “Gene could charm the birds off the trees, although birds were never his particular quarry--women were, the richer and more beautiful the better, and I never knew one who could resist him. I know I couldn’t.”

Loy is more than an accomplished stage and television actress--two acting arenas she entered well after she was 40. What may come as news to many readers is her longtime political activities, her commitment to causes. She supported and spoke on behalf of American Assn. for the United Nations; she visited hospitalized soldiers and stood up to Sen. Joe McCarthy; she actively campaigned for Adlai Stevenson and Eugene McCarthy in their separate runs for the presidency; and she worked untiringly for more than a decade on behalf of civil rights legislation. All this from a Montana-born redhead who moved with her widowed mother to Culver City as a teen-ager, attended Venice High School, posed for the statue outside the school and wanted, more than anything else in the world, to be another Isadora Duncan.

And she’s not done yet. Despite two major surgeries in the late ‘70s, she has this to say about her attitude toward life: “Whenever I sit down for any length of time, something inside my head starts nagging at me. I have got to keep on the go, keep working. I have been working since I was seventeen, and I am certainly not prepared to quit yet.” Myrna Loy is 82.

The book is brightened by 147 photos, all clearly captioned. The kind of care that obviously went into this book is the kind of care Myrna Loy seems to have given to everything she’s done in life.