TRUST YOUR HEART An Autobiography By Judy Collins Houghton Mifflin. 275 pp. $18.95

It hardly seems possible that Judy Collins -- who along with Bob Dylan, Joan Baez, Arlo Guthrie, Pete Seeger, Peter, Paul & Mary and others sang us through the '60s -- is herself now almost 50. The songs she sang are well enough known: 22 albums, six of them gold, some of them classics of contemporary popular music. Now with this memoir, we have the story of the singer behind the songs.

Salient facts: Judy Collins learned to perform at the feet of her father, a blind singer and radio personality, a "master dreamer and gypsy." A gifted classical pianist, Collins was 15 when she fell in love with folk music. "Singing for people ... Standing up in front of the audience, looking out at them instead of just sitting behind the piano and playing, I had the sense of eyes, faces, hopes ..." Folk music, she found, was more than music, it supplied the missing half, the story.

At 19 she left school, married, had a son. There was divorce, a custody fight, which she lost, and a career that took off. Along the way she had polio, tuberculosis and a throat operation; she fought alcoholism and lost love. An interesting inverse relationship, in fact, appears between her career and love life. As the career prospered, her love life suffered, and her loneliness is palpable through much of this account. Collins' relationships with Stacy Keach, Stephen Stills (who wrote "Suite: Judy Blue Eyes" for her) and others did not last. The stresses of a performer's life contributed, but Collins herself was a wanderer. She left her husband, she explains, because like a firefly that dies when captured, she wanted to be free "to light up among the trees, mysteriously." Her "ambivalent, careening experience with men" changed when her career began to slide, and she formed a stable, long-term relationship.

Less a memoir of the times than one woman's story, "Trust Your Heart" bears a few -- but only a few -- markings of the celebrity autobiography, such as the torrent of names. In the space of two rather short sentences, Collins manages to squeeze in 11 names. But much of the quotidian detail of her high-flying life is undeniably fascinating. The gifts she gives, for example: a silk scarf to Ned Rorem; a first-class trip to Hawaii for her parents after her first big record; peach-colored roses to her brother, who at 5 wished for a bush of peach roses in their yard; and for her true love, cuff links of amethysts and moonstones.

There are vivid moments in this book. One of my favorites occurs when the singer is on tour in North Dakota, and must wend her way back and forth from hotel to stage door in black high heels through an alley of deep, drifted snow. A second comes when she remarks of her beloved, baffling, driven, alcoholic father: "I often felt not that he was blind, but that I was invisible."

And finally, how it is to sing: "The singer must be like a swan gliding on the surface, feet paddling like mad beneath the water. There should be no strain in the lyrics, the eyes, the mouth or the muscles of the neck. Only beneath the chest bones, where the power goes deep down to the pelvis, are the muscles hard at work -- a solid, breathing, secure structure, invisible and invincible." The reviewer, who was managing editor of The Phoenix in the early '70s, writes frequently for Book World