Denise Brown recalled a time when her ex-brother-in-law, O.J. Simpson, lost control during an argument with his ex-wife and her sister, Nicole Brown Simpson.

"He went absolutely berserk," she said in an interview last month with ABC's Diane Sawyer. "It was a person that I had seen go from O.J., nice guy, to a person I never even knew. His whole physical being, everything changed, the look in his eyes -- and pictures started flying, clothes started flying. He ran upstairs, got all her clothes, started throwing them down the stairs... . He grabbed her, threw her out of the house."

Until now, pretrial hearings in the murder case against O.J. Simpson have concentrated on physical and circumstantial evidence -- the bloodstains found in his car, house and clothing, the timing of the killings of his ex-wife and her friend, Ronald L. Goldman -- and on the tedious selection of a jury to hear what is certain to be one of America's most protracted and celebrated trials.

But with Wednesday's hearing on domestic violence, the case shifts into different territory. For the first time, the legal focus will be on the tangled, ambivalent relationship between the Simpsons and the outbursts of rage such as the one Denise Brown alleged. Superior Court Judge Lance A. Ito must rule on whether to admit evidence that O.J. Simpson repeatedly abused his wife during their 15 years together and the two subsequent years between their divorce and her murder.

To convict O.J. Simpson, legal experts say, prosecutors will seek to show that it was his blood at the murder scene and that he had enough time to commit the crime and catch a flight to Chicago. But they also will seek to convince the jury that the outwardly affable former football superstar was in fact an abusive and occasionally violent husband, whose rage -- especially during the two years between the divorce and Nicole Simpson's death -- intensified until finally it became homicidal.

In recent weeks, Nicole Simpson's parents and sisters have dropped their reticence and have accused O.J. Simpson of beating her and threatening to kill her. O.J. Simpson has pleaded not guilty and has claimed that it was he, more than his ex-wife, who was the abused spouse in their troubled relationship. Defense attorneys have said family members are making wild accusations against O.J. Simpson to assuage their grief.

Prosecutors intend to introduce photos of a battered Nicole Simpson that they found in her safe deposit box, which they drilled open. They have filed a 1,044-page brief about O.J. Simpson's treatment of his wife, including a 64-page statement from Faye Resnick, author of an explicit book about Nicole Simpson's last years. Ito said last week the brief outlines "two dozen discrete issues and incidents."

Friends and family members say Nicole Simpson sought to break free from her allegedly abusive husband during the last few years of her life. As she did, they say, O.J. Simpson seemed to become more desperate and more determined to stop her.

O.J. Simpson stalked Nicole and the men she dated, noting her daily schedule in a notebook, showing up at her dates and, at least once, peeking at her through a window while she had sex with another man, according to grand jury testimony and information compiled by a private investigator hired by supporters of Nicole Simpson. There were heated arguments between the Simpsons, and at least one 911 phone call to police when O.J. Simpson threatened to break down Nicole's back door.

But the portrait of a collapsed marriage is complicated by the fact that Nicole Simpson herself often seemed ambivalent about her quest for independence. On at least one occasion, friends say, she attempted to reconcile with her ex-husband. Her family has indicated in court papers that she moved back into O.J. Simpson's Brentwood estate for several weeks before concluding last May that the relationship was beyond repair. A few weeks after she moved out for the last time, she was killed.

Nicole Simpson's friends and relatives say she was dependent, both emotionally and financially, on her wealthy and handsome husband. In the 1992 divorce papers, she testified that he often told her what to wear and how to look. There were many other women; by all accounts O.J. Simpson reveled in the celebrity life and its perquisites, sexual as well as financial. Theirs was a passionate and tempestuous relationship. There were public screaming matches, often triggered by Nicole's anger over her husband's extramarital activities. She made at least nine 911 calls to obtain police help and on one occasion in 1989 he battered and bruised her to the point that she needed medical treatment.

Friends and family say she gradually grew fed up with the physical abuse and the philandering. It took her years to work up the courage to make a break, they say, but in February 1992 she insisted on a formal separation. Eight months later, the Simpsons were divorced.

Part of the reason the breakup was so tortuous was that Nicole Simpson couldn't make up her mind, especially when pressured by O.J. "I've always told O.J. what he wants to hear," she stated in a deposition at the time of the divorce. "I've always let him -- it's very hard to explain."

Even during the divorce proceedings, Nicole Simpson found herself relenting to O.J.'s demands. When she filed on Feb. 6, 1992, Nicole asked to be allowed to drop her married name, a move that O.J. fought. When the papers were signed, she kept the Simpson name.

Therapist Susan Forward, author of the book "Men Who Hate Women, and the Women Who Love Them," who saw her twice after the breakup, recalled that Nicole Simpson said she was increasingly afraid of O.J. He had beaten her in the past and he was stalking her "in the bushes all the time," phoning her as often as 30 times a day and making threats to kill her.

"He had said to her: 'If I can't have you, I'll kill you,' " Forward said.

"I asked Nicole: 'Who knows about the beatings, the stalking, the murder threats?' She said, 'The police, my parents and several of my friends.' " But when Forward suggested that Nicole break all contact with O.J., Nicole recoiled. "I can't hurt his feelings," she told Forward.

Once separated, Nicole experimented socially. After she tucked her children in bed and left them with a babysitter, she went to drink and dance at bars. She dated a few men and confided to a handful of close female friends about her fears.

"O.J. was jealous," Kris Jenner, the wife of athlete Bruce Jenner, said recently in an interview with ABC News. "O.J. was jealous of the people that she would associate herself with if they were male. It took him awhile to get used to the fact that she was now dating and she had every right to go out and date. She was divorced. They had a passionate relationship. So to disconnect from that was very difficult for him."

One man who said he witnessed firsthand O.J. Simpson's possessiveness was Keith Zlomsowitch, a restaurateur who dated Nicole soon after the couple separated. Zlomsowitch last summer told a grand jury investigating the killings that in a one-month period an angry O.J. showed up unexpectedly during several of his dates with Nicole, according to a transcript released by the judge.

Zlomsowitch recalled that in early April 1992 he had invited Nicole Simpson to visit his restaurant in Beverly Hills. Within minutes of her arrival, O.J. walked in, walked directly over to where she was sitting with Zlomsowitch and some friends, leaned "quite imposingly" on the table and spoke in a "serious if not scary voice."

"I'm O.J. Simpson and she's still my wife," Simpson told Zlomsowitch. Nicole left for about 10 minutes with O.J., who then left the restaurant. Zlomsowitch said Nicole was upset and he himself "was obviously shaken a little bit by the ordeal."

Another time, Zlomsowitch recalled, he took Nicole Simpson and friends to a restaurant called Tryst. Within a minute of their arrival O.J. walked in, "looked at everybody at the table and made it very clear" that he was there, then pulled a chair from an adjacent table, turned it around to face them and "sat down and just stared" throughout their dinner.

"I was ... I was scared. I was shaken," Zlomsowitch recalled. Nicole appeared "very, very nervous." She finally spoke to O.J. for a few minutes, and then she left with Zlomsowitch.

But Zlomsowitch told the grand jury he was most worried by something that happened the night he took Nicole to the Improv comedy club in Hollywood. Nicole told him that she saw O.J. there; Zlomsowitch did not. But the two decided to leave for her town house.

After they arrived, they had sex on the living room couch. Zlomsowitch left after a few hours and returned the next day to see Nicole as her children played in the house pool. He was talking to Nicole and massaging her neck when, he said, O.J. walked into the home unannounced.

"I can't believe it. I can't believe it," O.J. said to the two of them. "Look what you are doing. The kids are right here by the pool."

Zlomsowitch testified that he and Nicole were startled speechless. Then O.J. told them: "I watched you last night. I can't believe you would do that in the house. I watched you." Zlomsowitch said he walked into the living room and noticed the drapes were open. O.J. followed him saying, "I watched you. I watched you. I saw everything you did."

Zlomsowitch told the grand jury his romance with Nicole ended soon after that episode.

For 13 months Nicole Simpson tried to break free from O.J. But in early 1993, she embarked on an attempt at reconciliation. They began seeing each other again that March. They took vacations together, and she was again seen on his arm at celebrity gatherings.

But the old problems remained. Friends say Nicole suspected that O.J. was still seeing other women. He remained jealous of the men she had dated.

O.J. Simpson complained that Nicole's ambivalence left him twisting. He told her friend, Cora Fischman, who spoke to ABC News, that "one day she wants me in the relationship, one day she doesn't want me in the relationship... . I don't know what she wants me to do."

In October 1993, a furious O.J. Simpson broke down the back door to Nicole's town house. On a 911 tape, he is heard shouting about a National Enquirer story about them and a photograph of Nicole and Zlomsowitch he found at her house.

Veteran private investigator Robert W. Peterson, who was hired by four individuals who consider themselves supporters of Nicole Simpson, said that by late 1993 O.J. was stalking Nicole again.

Peterson, whose work tracking down debtors in the savings and loan scandal won him praise from federal investigators, said he has verified that O.J. Simpson kept notebooks tracking Nicole's movements. In the last month of her life, O.J. had also begun watching her good-looking young friend, Ronald L. Goldman, a 25-year-old waiter who had befriended Nicole at a local gym, Peterson said. At least three times in May, friends of Goldman told the investigator, O.J. Simpson suddenly appeared at places where he was socializing.

Last May 8, when Nicole Simpson wrote a will, she underscored her resolve to separate permanently from O.J. She sent O.J. keepsake videos of their wedding and the birth of their first child along with a handwritten note saying she was severing communication. From then on, she told him, they could communicate through his personal secretary. A few days before she died, Nicole put on the market the pink stucco town house where she and her two small children lived.

Her family, who at first refused to describe Nicole Simpson as battered, in the past few weeks has said Nicole "lived in a private hell." Denise Brown, her sister, said in a statement, which she read on behalf of the family on the syndicated show "Geraldo," that Nicole "did her utmost to convince us to ignore the objective evidence and believe her protests that all was well." Lately, Denise Brown has added that Nicole warned that O.J. would someday kill her -- and that he would get away with it because no one would believe that such an affable media celebrity could do such a thing.

Nicole Simpson said something similar about 10 days before Christmas 1993 to Cyndy Garvey, ex-wife of former baseball star Steve Garvey, when the two women ran into each other at a shopping mall in Brentwood.

Nicole said she had just read Garvey's book, which discussed her abuse as a child, and said she admired how Garvey had raised her children despite the public nature of their family life.

But then Nicole took the conversation down a different track. "If they won't believe you, they won't believe me," she told Garvey. Referring to O.J., she added: "He's so charming. He's so charming. They just wouldn't believe me."

CAPTION: NICOLE BROWN SIMPSON'S LIFE

* 1959: Born May 19 in Frankfurt, Germany, of an American father, Lou Brown, and Juditha "Judy" Baur Brown, a West German mother. She is one of four daughters; her sisters are Denise, Dominique and Tanya.

* 1977: Shortly after graduating from high school, Nicole Brown, reared in Laguna Beach, Calif., meets O.J. Simpson. They move in together the following year.

* 1979: O.J. Simpson and his first wife, Marguerite, divorce.

* 1985: Nicole Brown and O.J. Simpson marry in February and have their first child, Sydney, eight months later.

* 1988: Their son, Justin, is born.

* 1989: Nicole Simpson calls police on New Year's Day, after she suffers a bruised neck, a split lip and a blackened eye. O.J. Simpson pleads no contest to battery.

* 1992: Nicole Simpson files for divorce in February and is divorced Oct. 15. The couple retain joint custody but the children reside with Nicole 90 percent of the time.

* Oct. 1993: Nicole Simpson calls 911 operator after O.J. kicks in the back door of her town house, screaming obscenities and threatening her.

* May 8, 1994: Nicole Simpson drafts her last will and testament.

* June 12, 1994: Nicole Brown Simpson, 35, and her friend, Ronald L. Goldman, are murdered outside her town house.

SOURCES: Staff and news reports

CAPTION: Nicole Brown Simpson feared O.J., her family and friends say.