PHILADELPHIA (AP) _ He was Anne Sexton's psychiatrist. He told her poetry would make her well. So she wrote, pounding her way to a Pulitzer and praise. She called Dr. Martin T. Orne her ''new God,'' and for eight years years he heard her deepest fears. If she was a confessional poet, he was her confessor.

Now, nearly two decades after the poet's death, the confessor has broken the traditional confidentiality of the doctor-patient relationship and released audio tapes of Sexton's therapy sessions to a biographer.

Houghton Mifflin has set Sept. 1 for the release of ''Anne Sexton,'' the first complete examination of Sexton's life and work since she killed herself in 1974 by carbon-monoxide poisoning. The release date was moved up two weeks because of the controversy surrounding the book, according to publishing house spokeswoman Irene Williams.

The book written by Diane Wood Middlebrook is the only biography of a major American figure known to rely on material from private sessions with a psychiatrist.

In an opinion piece Tuesday in The New York Times, Orne defended his role, saying Sexton left the tapes with him to use as he saw fit to help others.

''Sharing her most intimate thoughts and feelings for the benefit of others was not only her expressed and enacted desire, but the purpose for which she lived,'' wrote Orne, who released the 311 hours of tape with the approval of Linda Gray Sexton, the poet's daughter and literary executor.

But the position of the American Psychiatric Association is that the family's approval is not enough, according to Dr. William Webb, past chairman of the association's ethics committee, who now acts as a consultant.

''Unless you have the explicit approval of the patient, then you are essentially operating on supposition, and supposition puts at risk all future patients of psychiatry,'' said Webb, president of a private psychiatric hospital in Hartford, Conn.

Middlebrook, a Stanford University English professor who spent 10 years researching the book, said the tapes told her little new about Sexton. Sexton wrote openly autobiographical poems about sex, incest, abortion, masturbation, menstruation and drug addiction.

But Middlebrook said the tapes gave her an intimacy and understanding she wouldn't have had otherwise.

''I wasn't aware of the depths of the pain and despair she would go through when she was at her worst,'' Middlebrook said.

The tapes' most important contribution was to show how Sexton used her psychiatric treatment in her poetry, Middlebrook said.

Sexton's therapy sessions were taped from 1961 to 1964. At the time, reviews were coming out for her first book, ''To Bedlam and Part Way Back.'' She also was writing a second collection, ''All My Pretty Ones,'' and beginning work on the third, ''Live or Die,'' winner of the 1967 Pulitzer Prize in poetry.

Orne, professor of psychiatry at the University of Pennsylvania and director of a unit of experimental psychiatry at the Institute of Pennsylvania Hospital, began treating Sexton in 1956 in Boston.

She was a suburban 28-year-old housewife who had a suicidal breakdown after her second daughter was born. He encouraged her to write poetry as a way of helping herself and others with similar pain.

In a 1962 poem, she says to Orne: ''But you, my doctor, my enthusiast, were better than Christ; you promised me another world to tell me who I was.''

Orne started taping their sessions because Sexton had severe memory problems that were blocking progress in her therapy.

''By listening to and being able to tolerate her own pain and anger on the audiotapes, and by developing the ability to recall emotional events that mattered to her, Anne was gradually able to deal with these emotions in her poetry,'' Orne wrote in a foreword to the biography.

Orne refused to be interviewed by a reporter and has not responded to written questions submitted at his request.

In the Times piece, Orne indicated that he released the tapes to Middlebrook because she had ''the integrity and qualifications to judge Anne's literary contributions.''

When Middlebrook finished the manuscript, she and Linda Sexton went through it page by page. She also cleared with Orne all material she attributed to him and revised her interpretations until he agreed they were accurate.

''We all felt satisfied that we had fulfilled our obligations,'' Middlebrook said.

Webb disagreed.

''The patient depends on trusting the doctor-patient relationship ... and that means forever,'' he said.