NEW YORK  —  John F. Kennedy Jr.'s beautiful wife, Carolyn, was cocaine-addled, obsessed with an ex-boyfriend and flew into violent rages against her husband, an explosive new book says.

The couple had separated and the frustrated John was on the verge of calling the marriage quits just two days before their fatal plane crash, according to the startling account of author Edward Klein.

"I want to have children, but whenever I raise the subject with Carolyn, she turns away and refuses to have sex with me," John told a friend only days before he, his wife and her sister Lauren Bessette died when the plane he was piloting went down off Martha's Vineyard July 16, 1999.

"We've become like total strangers," Klein quotes him as saying.

"I've had it with her! It's got to stop."

At the time, he was living in The Stanhope hotel and she was staying in their TriBeCa loft, according to the book, The Kennedy Curse: Why Tragedy Has Haunted America's First Family for 150 Years.

Klein was a longtime friend of Jacqueline Kennedy Onassis and has written two previous books about the Kennedys.

Excerpts from the new book - which run in the August issue of Vanity Fair - depict a relationship that started unraveling almost as soon as John and Carolyn exchanged "I do's."

Among its revelations:

* John once returned to their loft to find Carolyn sprawled on the floor "disheveled and hollow-eyed, snorting cocaine with a gaggle of gay fashionistas," Klein writes. "Without asking John's permission, Carolyn gave keys to their loft to some of her friends so they could come and go as they please."

"You're a cokehead!" John screamed at her, one of the people present that night told Klein.

Klein also recounts a tale told him by a staffer at George magazine who had dinner with Carolyn one night.

"She made at least a half-dozen trips to the bathroom and came back to the table with white rings around her nostrils," the staffer is quoted as saying.

"The next morning, John came in and asked me, 'Why did you keep my wife out so late?' And I said, 'A better question, John, is why your wife didn't want to go home.' "

* Just before their July 1996 wedding, Carolyn flew into hysterics because she couldn't get her $40,000 zipperless dress over her head.

The fashion disaster made the bride two hours late for the ceremony. Her tardiness - and her insistence on clomping across the beach in high heels - outraged her sister-in-law Caroline, setting the tone for their future prickly relationship.

* Early in the marriage, "it was clear to friends that Carolyn was cracking under the pressure" from paparazzi and the press, writes Klein.

"She displayed the classic signs of clinical depression . . . A few months after the wedding, she began spending more and more time locked in her apartment, convulsed in crying jags."

* John and Carolyn fought, and the battles were often violent.

"John told friends that he felt trapped in an abusive relationship," Klein says.

"One time he had to be rushed to an emergency room for an operation to repair a severed nerve in his right wrist. He tried to dismiss the injury as the result of a stupid household accident, but his friends knew better: They were certain that Carolyn was the culprit."

* Both had fiery tempers, which ignited at the mention of either's former paramours.

When Carolyn heard rumors that John was seeing old girlfriend Daryl Hannah, "she flew into a rage," Klein says.

And John feared his wife was cheating on him with a former boyfriend, Calvin Klein underwear poster boy Michael Bergin.

Bergin's former manager told Klein that he once encountered Carolyn - who was living with Kennedy but not yet married to him - hiding under the model's staircase. She was waiting until the coast was clear before heading to his room.

The two "continued a sexual affair" while Carolyn was dating John, the book says.

"Carolyn and I had a very intense love for each other," Bergin told Klein.

"And I know deep in my heart that she still loved me even after she married John Kennedy. Some things just don't end."

During a screaming match in 1999, Carolyn told John she was still sleeping with Bergin. It was a lie, Klein writes, but John believed her.

* In March that year, John - after persuading Carolyn to see a psychiatrist who then put her on anti-depressants - joined her in marriage counseling.

But "nothing worked," writes Klein.

"Around July 12, 1999, Carolyn stormed out of the marriage counselor's office when the therapist raised the subject of her drug use. Then, in a supreme act of rejection, Carolyn began to sleep in a spare room."

* Klein says Carolyn resented Kennedy's wide circle of friends.

"Carolyn couldn't handle that," a friend of hers told Klein.

"She didn't want to go out. She would ditch John's friends, not show up for dinner, refuse to go to people's houses or events. She burned a lot of bridges."

Meanwhile, Klein says, John reverted to his bachelor ways, "pumping iron late into the night, going off on kayak trips with the boys and (Carolyn suspected) playing around behind her back with the girls."

Still, those who knew Carolyn doubted she would ever leave John, Klein writes. And John, he says, was "besotted" with Carolyn from the moment he met her. "He lived and breathed Carolyn," a friend told Klein.

* As his marriage was disintegrating, so was the political magazine that he published, George.

A few days before his death, Klein says, John offered to sell the money-hemorrhaging magazine to Condé Nast. "John died before we could make a decision," said the publisher's CEO, Steve Florio.

The weekend of July 16 marked the wedding of one of John's favorite cousins, Rory Kennedy.

Though recovering from a broken ankle, he planned to pilot his $300,000 Piper Saratoga to the nuptials at the Kennedy compound in Hyannis Port.

"He had received medical advice not to fly for at least another 10 days," Klein writes.

What's more, Klein notes, a friend "expressed concern that John had become overconfident about his flying [and] urged John to view his broken ankle as a warning sign."

But John was determined to fly - with or without his wife.

"Gravely alarmed" that John and Carolyn were living apart, Lauren asked them to lunch, thinking they might be able to discuss their problems with her.

"The relationship between John and Carolyn had become so tense and ugly that neither of them was in the mood to talk," Klein writes. "They sat in stony silence."

But at the lunch, Lauren was able to convince her sister to fly to Rory's wedding that weekend. To encourage Carolyn, Lauren offered to fly with them as far as Martha's Vineyard.

On Friday, July 16, John and Lauren left Manhattan and headed for Essex County Airport in Fairfield, N.J. Traffic was bad, and they didn't arrive until after 8 p.m., and daylight was fading.

Carolyn hadn't yet shown up. Speaking publicly for the first time, hair colorist Colin Lively divulged to Klein the story behind Carolyn's delay.

"It was late at the end of the day on Friday, and [she] was right next to me, sitting in the same line of people getting pedicures," Lively recalled. "She had a little piece of sheer fabric - about 3 inches square, almost white with a hint of lavender - and she wanted her toenail polish to match the swatch."

After the pedicurist applied the polish, "Carolyn would go to the window and put her foot up and put the fabric next to it," examining the color, Lively said.

Three times, Carolyn had the pedicurist redo the color.

The entire time, her cell phone was ringing, and Bessette would answer it, the hairdresser said.

"'What?' she'd say impatiently into the phone," said Lively. " 'I told you I'm getting a pedicure . . . The more times you call me, the longer it's going to take!' "

Only when her nails were done to her satisfaction, Klein writes, did Carolyn Bessette Kennedy finally leave the salon.

John and Carolyn Kennedy and Lauren Bessette took off from Essex field July 16, 1999 at 8:38 p.m. The last signal from the plane was transmitted at 9:39 p.m. - about 20 minutes before it was due to land on Martha's Vineyard.