MICHELLE NYCE had just returned home from an after-work motel tryst with her lover when her notoriously jealous husband - whom she wanted to divorce - confronted her in the garage of their Hopewell Township, N.J., mansion early Friday morning.

What happened next would leave the raven-haired mother of three dead and her husband - a research scientist world-renowned for his efforts to cure asthma but plagued by a fondness for drink, according to in-laws - fighting for his freedom from a Mercer County jail, where he's being held on a murder charge.

Jonathan Nyce, 53, told police his wife had lunged at him with a knife, sparking a struggle in which he hurled her to the ground and pounded her head into the pavement while she continued trying to slash him. Her death, he told investigators, was an accident that resulted from self-defense.

But prosecutors say Nyce, furious that his wife would not end her yearlong affair, attacked her in a blind rage. The 5-foot, 100-pound Filipino had no chance against her husband, who stands 6-3 and weighs more than 200 pounds, prosecutors said. And police found no sign of a knife, which Prosecutor Joseph L. Bocchini Jr. called "a figment of [Jonathan Nyce's] imagination. "

Michelle Nyce confessed to the affair last summer, after an anonymous blackmailer contacted her husband, her family said.

The details of Michelle's slaying came out yesterday, when Nyce came before Mercer County Superior Court Judge Charles A. Delehey to plead for reduced bail.

Delehey agreed to cut bail from $2 million cash to $1 million cash on condition that Nyce forfeit his passport. He denied defense attorney Lee Engelman's request that Nyce be permitted to put his house up as collateral.

The court also later denied Nyce's application for a court-appointed attorney, saying financial need had not been proven.

Michelle Nyce's brother, Sonny Ragenil, said yesterday from his home in the Philippines that Michelle had been thinking of divorcing her husband because of his constant drinking and jealous rages. She also was upset when Nyce cut the amount of money he provided to her after he left his job, he said.

"He cut all the accounts of my sister," Ragenil added. "That's why my sister decided to go to work. She had no money to support family in the Philippines. "

He said that besides the constant arguing, Nyce drank heavily.

Ragenil said Nyce drank "almost every day, especially when they [were] on vacation" in the Philippines. "He always drank. "

He recalled that once they had been at a restaurant at a seaside resort and Nyce had been "mad at Michelle" because their tour guide had been friendly to his wife. "He was very jealous to everybody. "

Michelle's sister, Melodia Ragenil, who also lives in the Philippines, told the Daily News yesterday that their father had spent more than six months with the Nyces at their suburban Trenton home, returning on Jan. 9. He was unavailable for comment yesterday, she said, because of illness.

According to a published report, Jonathan and Michelle met after he contacted an agency and got her picture. Sonny Ragenil said he did not know anything about the agency but that the couple's relationship began when they became pen pals.

At his bail-reduction hearing yesterday, against the advice of his attorney and the judge, Jonathan Nyce asked to make a statement.

"I have no history of physical violence ever against any person," he said somberly through closed-circuit television. "I never ever had ill will toward my wife at any point. This, what happened, was a pure accident. "

Whether Michelle's death was accidental, prosecutors presented evidence yesterday that makes it clear the cover-up was not.

Michelle, 34, was found in the driver's seat of her 1997 forest-green Toyota Land Cruiser at 8:45 a.m. Friday. A passing utilities-truck driver saw the SUV, its engine still running, submerged in a shallow, frozen stream off Jacobs Creek Road, less than a mile from the Nyce home. When he stopped to investigate, he found Michelle dead behind the wheel.

Responding police officers found snowy footprints leading away from the passenger-side door and toward the Nyce home, assistant prosecutor Tom Meidt said yesterday.

When questioned, Nyce denied involvement in his wife's death, told police about his wife's affair and accused her lover of killing her, Meidt said.

But under continued questioning, he admitted he had killed her when she returned home from her tryst at an area motel at 12:30 a.m. Friday and then staged the wreck, Meidt said.

He told investigators he had put his bloodied wife in the driver's side of her car, climbed in the passenger side and used an ice scraper to depress the gas pedal and drive from their hilltop home to the curvy Jacobs Creek. But police doubt that story, saying the driver's seat had been pushed back as far as possible - a position suited more to Nyce's stocky build rather than his petite wife's.

Police also found blood had been spattered and smeared in the garage where Michelle typically parked, Meidt said. Blood also trailed up to a second-floor bathroom, where Nyce presumably cleaned himself up.

Investigators found bloody paper towels and a blood-soaked sock in a trash can, empty bottles of peroxide and a trash bag containing blood-soaked towels stuffed up the basement chimney-trap, Meidt said.

And they found chopped-up shoe soles in the basement, which when reassembled matched the tread of footprints found at the creek site, Meidt said. Nyce also had some "markings [wounds] on his hands" that he could not explain, Bocchini said.

Bocchini declined to pinpoint when Michelle died or discuss whether she could have survived if her husband had sought medical treatment for her.

Nyce learned of his wife's affair in July, prosecutors said.

Jonathan Nyce received an anonymous letter last summer seeking $500,000 in exchange for "information" about his wife, Michelle's family told the Trenton Times yesterday. The letter prompted Michelle to confess the affair to her husband, her relatives said.

But Bocchini said investigators had not found any evidence of such extortion attempts. Police did respond to the Nyce home in July, when Michelle complained she had received a harassing phone call. Authorities refused to discuss the caller's identity or the topic of the call, saying only that the harassment complaint was unfounded.

Investigators also are considering financial troubles as a possible motive.

The family finances "were not necessarily as strong as one would believe in looking at the house," Bocchini said.

The Nyces listed their $1.6 million house for sale three months ago, and Nyce had been unemployed for almost a year. He had been chief executive officer and chairman of EpiGenesis Pharmaceuticals Inc. in Cranbury, N.J., until he left last March, when the company "changed direction," Engelman, Nyce's lawyer, said. He continued to receive "monthly sums of money" from the company, which he founded in North Carolina in the mid-1990s.

Nyce's parents and brother, who live in Collegeville, Montgomery County, and are caring for the couple's three young children, were in court yesterday but declined to comment.

The case now goes before a grand jury for indictment. Bocchini said he had not decided whether to pursue the death penalty.

Engelman said Nyce still cannot afford the reduced bail, because his money is tied up in his home and other items. Engelman said he would seek another bail reduction "as soon as possible. "

"He is not a flight threat. He has strong ties to this area and the Delaware Valley in general," Engelman said.

Engelman suggested that Nyce, even before his wife's death, was the primary caregiver of the couple's children, saying: "His children need him more than ever. He has never harmed his children . . . There was really no one else who provided appropriate care for those children. "

Nyce attended Temple University, earning a bachelor of science degree, a master's degree in molecular biology and doctorate in pharmacology.

Nyce, who helped to develop a drug that helps prevent asthma attacks, holds several patents, Engelman said.