Steven Bach's "Dazzler," from Alfred A. Knopf, is chock-full of juicy details about Hart's homosexuality, battles with manic-depression, suicidal impulses and spendthrift ways.
Kitty Hart refused to be interviewed for the book, but is said to have obtained an early proposal for it, and asked her wide circle of friends not to cooperate with Bach.
Yesterday she told The Post: "I really have nothing to say about the book. You know, my dear, life isn't always a bed of roses."
"Dazzler," a copy of which was obtained by The Post, chronicles Hart's spectacular rise from the tenements of the Upper East Side to fame and fortune on Broadway as co-author, with George S. Kaufman, of the classic comedies "Once in a Lifetime," "You Can't Take It With You" and "The Man Who Came to Dinner."
Hart himself covered some of that terrain in his celebrated autobiography, "Act One," but as "Dazzler" reveals, that memoir was very much a romantic account of a troubled life.
Hart certainly did not address the issue - for years spoken of sotto voce in theater circles - of his sexuality.
Bach tracks down ex-actors and chorus boys, who claim to have had affairs with Hart.
His first fling may have been with an older actor named Lester Sweyd, who became the young writer's mentor.
"Here's that picture - sleep with it next to your heart," young Moss wrote on a self-portrait he gave to Sweyd.
The older man added a caption of his own: "A Dirty Mind Is Perpetual Solace."
Jess Baker, who played the male ingenue in "You Can't Take It With You," tells Bach he had difficulty acting his role because night after night Hart sat in a box seat staring at him with "frank sexual interest."
Hart briefly lived with a handsome young actor named Glen Boles, who says, "Moss was consumed with efforts to find his sexuality. He was sexually active . . . but sexuality was less important to him than wanting to love and be loved. He used to say: 'If I could love somebody, I wouldn't care if it was a man, a woman or a pig!'"
Bach - who wrote "Final Cut," a superb book about the making of the Hollywood bomb "Heaven's Gate" - suggests Hart may have had an affair with Cole Porter. He was also attracted to Robert Goulet, whom he (briefly) directed in "Camelot."
"Thank God I had my heart attack and could get out of 'Camelot,'" Hart is quoted as saying. "It was the only way I could keep from being tough on Robert Goulet and taking out on him how much I resented him for being so attractive."
Agnes De Mille, a first-rate gossip with a dagger for a tongue, referred to Hart as a "known homosexual." She choreographed the 1943 military show "Winged Victory," which Hart directed, and accused him of "openly carrying on with boys in the company who flirted outrageously with him."
Later in life, Hart sought treatment from the famous crackpot psychoanalyst Lawrence Kubie, who claimed he could "cure" homosexuality.
Around that time, Hart married Kitty Carlisle, who Bach claims, banished from their Bucks County country house the hordes of young men who used to sunbathe naked by Hart's pool.
Bach, who gained access to Kitty Hart's as-yet-unpublished oral history, quotes her as saying she was not in love with Hart when she first married him, nor was he with her.
"It was the right step for the right people at the right time," Bach writes. "It was suitable. The love part would come later."
"Dazzler" also details Hart's frequent slides into depression (fought off, in some cases, with shock therapy) and his candid letters to Dore Schary about suicide.
"I came very close to putting an end to it all," he wrote Schary in 1938. "But I threw the stuff away."
Hart, as Bach shows, was free and easy with his money, spending great sums on friends, family and himself. When he died, of a heart attack in 1961, he left an estate of just $500,000, despite the fact he wrote and directed some of the most successful plays and musicals of all time, including "My Fair Lady."
"Dazzler" is not all salacious gossip, of course. It presents a richly detailed, extremely sympathetic portrait of Hart, whose life, Bach writes, was one of "uncommon generosity in an often mean-spirited world, a life more painful than we knew and maybe a braver one, too."
Bach also analyzes Kaufman and Hart's famous plays, and tries to answer the one question both men always declined to discuss: Who wrote what?
He concludes: "The only surviving original draft that gives definitive clues is Moss' first version of 'Once in a Lifetime,' in which the wit and originality were apparent before Kaufman became involved. Kaufman sharpened and polished 'Once in a Lifetime' to Broadway standards, and did the same with Moss.
"Their best work together was more than the sum of their parts; it was a whole in which wit joined feeling, and it produced two enduring comedies, 'You Can't Take It With You' and 'The Man Who Came to Dinner.'
Kaufman gave Moss first billing on both of those plays, which speaks to professional fairness, and to Moss' sometimes inspired contribution to their best work."