NY- The father of journalist Peter Braunstein - the prime suspect in the phony-firefighter Halloween sex attack - urged his son to turn himself in yesterday.

"He's disturbed and he needs help badly," gallery owner Alberto Braunstein told the Daily News. "I want to believe he's not guilty, but you have to be deeply disturbed to do what he's done."

"I can't believe it, yet I must believe it," said Braunstein, who has been estranged from his son for two years. "This is not the first time he's had problems."

No charges have been filed against the younger Braunstein, but sources said police want to grill him about a vicious Halloween attack in which a pervert dressed as a firefighter set blazes in a Chelsea building to get into a woman's apartment.

Drugging her with chloroform, the attacker sexually abused her for 13 hours before leaving with a videotape of the violation and a pair of high heels as a trophy, sources said.

Tipsters identified Braunstein, 41, as a suspect because he resembles a sketch of the predator and his ex-girlfriend is an editor at the fashion magazine where the 34-year-old victim once worked.

Police quickly discovered Braunstein had a sadistic history: He is on probation after pleading guilty this summer to menacing the ex-girlfriend.

She accused him of taping her to a chair while he toyed with a knife, deluging her with threatening E-mails and calls, and posting nude pictures of her on the Internet. "I will destroy you professionally and otherwise," he allegedly told her.

His father said he doesn't know where his son is, but he wants him to come out of hiding.

"All I can do is urge him to turn himself in," he said. "He can't defend himself if he doesn't turn himself in."

Braunstein is a prolific writer who specialized in '60s and '70s culture. He has worked at The Village Voice and Women's Wear Daily and edited a 2001 book, "Imagine Nation."

"I know him as one of these people who is very charming and has a way of impressing you with his brilliance," said his co-editor, Michael William Doyle.

"Of course, he's also subject to moods."

Though always edgy, after the 9/11 terror attacks Braunstein suffered a breakdown and his behavior became even more erratic, a friend said.

"He was always borderline," the friend said. "But something snapped in that guy."

Braunstein got fired from Women's Wear Daily in 2002 and couldn't find another writing job. Then his relationship with the fashion editor disintegrated. He wound up in the Bellevue Hospital's psych ward after he cut himself and tried to blame her.

In the summer of 2004, he mounted an Off-Broadway play about Andy Warhol and Edie Sedgwick, but seemed more consumed with ruining the name of his ex-lover. The play's Web site contained links to poisonous screeds about the woman, whose name is being withheld by The News.

"It's the nasty truth of how art is created: through a crucible of pain, suffocating neglect, paranoia, and malice that wrecks some spirits - but propels others to astounding heights," one posting read.

The play was a flop, fraught with problems from the start.

The first producer, Drew Figueroa, the head of a downtown theater company, withdrew his support because he thought Braunstein was "dangerous."

The manager of another playhouse where the show eventually was staged called Braunstein "crazy, chemically unbalanced."

A cast member also said the playwright appeared unhinged and peppered his conversations with sex and drug innuendos.

"He used to call up girls in the cast in the middle of the night and wanting to meet up in a bar," said the woman, who asked not to be identified.

"He was always looking like he just got out of bed. I remember he once bragged about how he had been on a cocaine binge. He was a nut job."

Another actress said Braunstein left her so many unsettling E-mails and voice mails, she went to police - but didn't press charges because she feared retribution. "I wanted to leave the play but I was actually afraid to," she said.

Braunstein's 72-year-old father said it was an offhand comment about the play that drove a wedge between him and his son.

"He said, 'Look at all the things I've accomplished and now I'm producing a successful Off-Broadway show.'"

"I said, 'It's not successful yet.' We had words. He got up and left. He said he didn't want to ever see me again."

When detectives first visited Alberto Braunstein on Friday, he seemed skeptical his child was the man in the police sketch. But by yesterday, he was all but convinced his son was the culprit.

"You don't choose your parents and parents don't choose their children," he said.

Additional: The beautiful escort touted this year as New York's No. 1 hooker was among the women in Peter Braunstein's life.

Natalie McLennan, who bragged she charged $2,000 an hour as a call girl, was briefly cast in Braunstein's failed play, "Andy and Edie" last year.

Several cast members said there was talk that McLennan and Braunstein were romantically involved after someone claimed to see them canoodling at a downtown bar.

McLennan, who had a small part in the Andy Warhol play, dropped out of the production well before the curtain rose.

But she ended up starring in a real-life drama after she posed for a New York magazine cover story on the city's top escort.

The auburn-haired beauty boasted of a client list that included a professional quarterback and Wall Street bigwigs.

She's kept a lower profile since being sprung on $50,000 bail following her September arrest for prostitution and money laundering. She could not be reached for comment yesterday.

Braunstein's father, Alberto Braunstein, said his son never had trouble finding a girlfriend, despite his emotional problems.

"He's very charming," the dad said. "He's very engaging and he has a sense of humor, so it was always very easy for him with women."