PETER BOGDANOVICH says he never had a chance to fail in private.

Given the chance to mourn behind closed doors, he has chosen to go public with "The Killing of the Unicorn," an intensely personal version of the brutal torture-slaying of Dorothy Stratten, the golden-haired, 20-year-old former Playboy Playmate of the Year who became his lover in the last four months of her life.

It is a curious exercise for a man who vows that his life is not an open book, one that prompted reviewer James Wolcott in Vanity Fair to comment that the once-celebrated director of "The Last Picture Show," "Paper Moon" and "What's Up Doc?" seems "to have flipped his beanie."

It took him three years to write the book, he says. He went through five drafts. He stopped making movies, stopped going out, stopped dating. He also stopped being so arrogant.

He says the lights blink on and off at strange times and he knows that it's Dorothy. Trying to tell him something.

He says the time he spent with her was the happiest in his life, happier even than his years with Cybill Shepherd.

He says he is still in love with her. Dorothy, not Cybill.

"People would like me to put it behind me," he says quietly. "I don't know what that means."

He sits down to a lunch of tuna fish on rye, iced tea and a flip-top box of Marlboros. He is tall and neatly groomed and looks younger than his 45 years, with a tapered, Beverly Hills haircut and a thin gold neck chain peeking through an open shirt. He is smooth. Charming. Wearing a casual jacket and a mournful chipmunk expression.

He talks for 90 minutes, then calls the interviewer at home the next morning and talks for an hour. He'd been thinking about the questions. He wanted to give "better answers."

"One of the main things that happened as a result of the murder," he says, his voice cracking, "is that I refuse to take anything for granted any longer. I started questioning everything. I thought I'd either go nuts or I'd get an answer to some things."

He talks about the exploitation of Stratten: Bob Fosse's film "Star 80" (for which Mariel Hemingway underwent silicone implants) and a made-for-television movie,"Death of a Centerfold," starring Jamie Lee Curtis.

He says it was time to tell the real story.

He knows the critics have been unkind. He knows he is being accused of exploiting her memory as much as the other two commercial ventures, and he bristles at the comparison.

"I think that's fairly hypocritical," he says. "First of all Hugh Hefner certainly exploited her body and talent and charm for the greater glory of Playboy. Bob Fosse and that television movie certainly exploited the story without knowing what the story was. I don't believe I'm exploiting her in any way by telling her side of the story."

Stratten is portrayed by Bogdanovich as an innocent victim of the Playboy machine who wrote schoolgirl poetry, ordered plastic toys from the back of the Raisin Bran box, made love with the lights out and hitched herself to the hustling Paul Snider, her husband, manager and eventual murderer, because she hated her father. The book also suggests that Playboy publisher Hugh Hefner made life miserable for Stratten after she rejected a pass from him one night in a hot tub.

Hefner disputes parts of Bogdanovich's book and, according to the author, tried to stop publication of "The Killing of the Unicorn." Hefner has told UPI he is contemplating filing a lawsuit, although he doesn't want to call any more attention to the book.

Reading "The Killing of the Unicorn" -- profits from which will go to Dorothy Stratten's estate -- is akin to reading someone else's diary. Intimate details of lovemaking are interspersed with adoring prose that threatens to canonize the Canadian-born bombshell:

On that afternoon, in the park and back in my suite, when Dorothy and I finally made love, we found what we had been searching for all our lives. We truly made love; creating it again for each other, discovering it together for the first time . . . I could hardly believe she was there, that she really existed, that she wasn't a dream. There was something miraculous about Dorothy Stratten, something not altogether of this world.

Such passages prompted James Wolcott to ask, "How can he write such doodle?" and to conclude that "what Dorothy Stratten deserves above all else is a measure of rest."

Bogdanovich flushes.

"To let her rest is to let her rest as a dumb blond, which is how she was portrayed by everybody," he says. "A dumb, maniputable [sic] blond who didn't have any guts and who was pushed around by a lot of guys."

He says he never doubted his mission. "I think writing the book helped to get some of it out. It was kind of a journey of discovery about her and about myself."

But the love affair lasted barely four months. In fact, the relationship seemed to be souring during the last days, a shift in the emotional winds that Bogdanovich now theorizes was Stratten's premonition of her own death.

I got into bed beside her, her warm skin next to mine. We embraced gently and began to kiss again. Even here, in the dimmest light, under the covers, she was not enjoying the lovemaking as she always had before. This was the second day in a row that things did not seem right, and tonight they seemed worse.

The next morning, Bogdanovich prepared breakfast -- cottage cheese and yogurt -- and Stratten reprimanded him for talking with his mouth full.

Bogdanovich, a successful film critic before turning director, is no stranger to publicity over his private affairs. In 1972, he left his wife Polly Platt (the mother of his two daughters) for 18-year-old Cybill Shepherd, a former Glamour cover girl whom Bogdanovich cast in "The Last Picture Show." He made two more critical and commercial successes, "What's Up Doc?" and "Paper Moon" (winning Tatum O'Neal an Academy Award), before turning out a string of box office failures, "Nickelodeon," "Daisy Miller," "At Long Last Love" and "Saint Jack." His last film, "They All Laughed," featured Dorothy Stratten, and was also a financial and critical failure. His new film, "Mask," starring Cher, will be released later this year.

After Shepherd left Bogdanovich to marry a man from her home town, he says he "went through a period of promiscuity . . . but Dorothy ended all that. I prefer a monogamous relationship if I can find one."

The period of promiscuity Bogdanovich refers to coincided with the nights in which he was a regular visitor at Hefner's mansion. He met Dorothy Stratten there, a fact he seems to overlook in his consciousness-raised zeal to condemn the Playboy life style as demeaning to women.

Yes, he says, he is a changed man.

"I feel like I've changed completely in the last four years. I've also tried to change actively. I've become more aware of certain things. I certainly had an arrogant streak. And I certainly was defensive in certain cases. Maybe I'm still arrogant, but I try not to be.

"I understand women better than I ever did. And I think I understand the relations between men and women better than I used to."

He lights a cigarette, fiddling with the matches. "Cybill and Dorothy were about as different as two blonds can be. Emotionally, physically, mentally. There was no comparison between the two of them."

He says that what attracted him to both Cybill and Dorothy was their "maturity."

But it wasn't, he insists, as if he had found another Cybill in Dorothy. "Hardly," he sniffs. "All of that is popular psychology. Love is a lot more complicated than people think. Teresa Carpenter wrote a very good piece in The Village Voice, but it wasn't right about Dorothy and it wasn't right about me because she didn't know her and she doesn't know me."

Carpenter, who portrayed Bogdanovich in her 1980 Pulitzer Prize-winning article as "one of a triumvirate of users," says, "For someone who professes to know Dorothy well, he didn't bring her character to life. It illuminated very little as far as I'm concerned."

Bogdanovich first met Stratten in October 1978, two months after she had left her job at a Dairy Queen in Vancouver and come to Los Angeles with Paul Snider, a hustler and sometime pimp who had "discovered" Stratten (then Dorothy Hoogstraten) and persuaded her to pose nude for Playboy. She and the director did not meet again until a year later, after she had married Snider and began working as a waitress at the Los Angeles Playboy Club.

In January 1980, Stratten was cast in her second film, "Galaxina" (her first, "Autumn Born," was a forgettable exploitation flick), and had already been chosen as Playboy's Playmate of the Year. Two months later, she flew to New York to join Bogdanovich on the set of "They All Laughed." By this time, Stratten had become estranged from her husband and the affair with the director twice her age was in full bloom.

"She was unhappy in her marriage and had been for over a year. I wasn't taking Dorothy away from her husband. Her husband had already lost her long ago. The reason it took Dorothy and me such a long time to really connect was because she had been burned so badly, she didn't want to make another mistake and I didn't want to come on to her because I knew that's all she had been getting so I was very laid back. I didn't want to be like every other guy."

He leans forward. "The week before the murder she went to see him, and had a tremendous fight with him and that's when she told him she was in love with me and that she wanted to be with me and that it was over."

The following day, Snider was informed that he was no longer welcome at Hefner's mansion. Snider became enraged. "He was convinced that Hefner, she and I had a threesome going on, convinced that that's where it was heading if it hadn't already been there."

On Thursday, Aug. 14, 1980, Stratten left Bogdanovich's house, where she had been living, and went to see Snider. That evening, police found a gruesome scene; Stratten had been tortured on a bondage machine designed by Snider, raped, sodomized and killed by a shotgun blast to the face. Snider died of a self-inflicted shotgun blast.

"I came to realize that she had been protecting me, protecting my children, protecting her family by what she did, but she felt that she could handle it and she also felt that she had to handle it because it was her problem, not mine and not anybody else's."

Still, it is Bogdanovich who feels responsible for her death.

"How could I not?" In retrospect he thinks he should have met with Snider. Smoothed things out. Offered him some money.

He has a multitude of regrets.

"I don't know how you get to be 40 without having a whole bunch of regrets. I think maybe you just don't want to admit it. I have many regrets. One of them is obviously that I didn't know more about myself and about women and society so I would have been smarter and quicker to act and to know. 'The only sin is ignorance.' I've tried since then not to be so damn ignorant."

He has finished his tuna fish sandwich and must leave for a radio interview.

The death of Dorothy Stratten, he concludes, was not a total loss.

"I found out," he says, "that a lot of the things that one hopes for in life were not really what they were cracked up to be, including money, fame and success. Dorothy gave me an incredible sense of hope and a sense that there was a reason for it, and that there was a lot to be hopeful and positive about, and she definitely renewed my life.

"Even in death."