THE O.J. SIMPSON MURDER TRIAL : Victim’s Tearful Sister Alleges Simpson Abuse : Trial: Denise Brown describes two incidents. DNA expert denies prosecution tampered with evidence.

In a brief but unforgettable appearance on the witness stand, Nicole Brown Simpson’s sister tearfully told jurors Friday that she saw O.J. Simpson publicly humiliate his wife and on at least one occasion violently attack her.

Under gentle questioning from Deputy Dist. Atty. Christopher A. Darden, Denise Brown spent 26 minutes on the stand, at first fighting but then eventually succumbing to her emotions. As the court day ended, she told the story of an explosive confrontation that she said occurred in the Simpson home after she accused Simpson of taking her sister for granted.

“He grabbed Nicole, told her to get out of his house,” she said. “Wanted us all out of his house, picked her up, threw her against the wall, picked her up, threw her out of the house. She ended up on her--she ended up falling. She ended up on her elbows and on her butt. . . . We were all sitting there screaming and crying. He grabbed me and threw me out of the house.”

In the weeks immediately after the murders, Brown denied that her sister had been abused, but more recently she has emerged as the family’s leading critic of Simpson, who she believes committed the June 12 murders of Nicole Simpson and Ronald Lyle Goldman. Simpson has pleaded not guilty.

On Friday, Brown came to court wearing two angel pins and an angel earring similar to jewelry worn by her deceased sister--as well as a black and white cross that dangled from a chain around her neck. As she described the violent scene at the Simpson house, she paused, overwrought and struggling to regain her composure.

“Are you OK, Miss Brown?” Darden asked.

“Yeah,” she responded. “It’s just so hard.”

In the audience, Lou Brown, the father of Denise and her dead sister, bowed his head silently, obeying Superior Court Judge Lance A. Ito’s order not to display emotion even as his oldest daughter testified about the alleged abuse of his second child. Simpson looked in Denise Brown’s direction, but did not display any emotion as his former sister-in-law broke down in tears. The jurors sat impassively as she sobbed.

Despite Brown’s sniffled insistence that she could continue, Darden asked that court be adjourned for the day, just a few minutes ahead of its scheduled conclusion. Ito agreed, sending the panelists back to their hotel for the weekend with the image of the emotionally spent victim’s sister--who bears a striking resemblance to Nicole Simpson--fresh in their minds.

In addition, they earlier heard another riveting tale from Brown, one that does not involve allegations of physical violence but that nonetheless raises questions about Simpson’s treatment of his wife. Describing a scene in a Santa Ana bar, Brown said her then brother-in-law grabbed her sister in front of a room full of strangers.

“At one point O.J. grabbed Nicole’s crotch and said: ‘This is where babies come from and this belongs to me,’ ” Brown recalled, setting her jaw and vainly attempting to choke back tears. “And Nicole just sort of wrote it off like it was nothing, like, you know, like she was used to that kind of treatment.”

“I thought it was really humiliating, if you ask me,” added Brown.

Brown will be back on the stand when court resumes Monday morning, and defense attorneys have painstakingly prepared for the delicate task of cross-examining her. In interviews since the murders, Brown has supplied Simpson’s lawyers with a rich vein of material to challenge her credibility, but capitalizing on it is a sensitive assignment since defense attorneys can ill afford to appear to attack her.

The task will fall to Robert L. Shapiro, who leads the Simpson defense team but who has been heard from only sporadically since Johnnie L. Cochran Jr. emerged as the principal trial lawyer. Legal experts said Shapiro’s cross-examination could prove one of the most important undertakings of the entire case.

“This is the dead sister in black hair,” Gerry Spence, a renowned criminal defense attorney, said of Brown. “How she comes off will determine what the jury thinks about the dead one. If she’s destroyed in cross-examination, that will bode ill for the prosecution.”

The defense’s wariness of Brown, who has openly expressed her view that Simpson is guilty of the murders, was evident even in Friday’s brief appearance. They objected often during her time on the stand, meeting with Ito and the prosecutors out of earshot of the jury. Afterward, they suggested that Brown’s emotion might have been an act.

“That’s one of the reasons we kept approaching the bench,” Cochran said outside court. “I saw it coming. We kept trying to say it was not fair.”

Asked what was unfair about a display of emotion, Cochran responded: “If it was planned, is that fair?”

Brown’s appearance on the stand capped a week of often dramatic domestic abuse testimony and concluded five days of problems for the Simpson defense. At the beginning of the week, jurors were told that Simpson’s lawyers had violated the law by withholding witness information from the prosecution. At the end, they heard about more allegations of domestic abuse and, for the first time, they were confronted with the human toll of the Brentwood murders that have riveted the nation’s attention for more than seven months.

Although Brown’s testimony was the emotional high point of the trial Friday, one of the prosecution’s DNA legal experts also strongly responded to defense allegations of evidence tampering--charges made during Cochran’s opening statement Monday.

In his comments to the jury, Cochran had suggested that police might have smeared blood from Nicole Simpson on socks found in O.J. Simpson’s bedroom. To support that theory, Cochran noted that a local television station erroneously reported DNA test results on that sock before any such tests were ever performed and suggested that someone in law enforcement thus had advance knowledge of the tests. That, Cochran said, was evidence of a “sinister” effort to frame Simpson for the murders.

But Deputy Dist. Atty. Rockne Harmon said Cochran had failed to mention--as The Times reported last fall--that while no DNA tests had been performed at the time of the television story, conventional analysis of the socks had been done in August and had produced results consistent with the blood of Nicole Simpson. That raises an alternative explanation for the television station’s false report--namely that either the station or its sources mistook the conventional blood test results for DNA analysis.

In addition, Harmon disputed Cochran’s suggestion that a Los Angeles police detective could have smeared evidence with blood from a sample that Simpson provided to police. In fact, Harmon said, all the evidence samples had been collected before Simpson ever gave police that sample.

To clear up any lingering doubts, however, Harmon offered to subject the reference samples of blood from O.J. Simpson and Nicole Simpson to additional testing. The samples contain a preservative that can be tested for, Harmon said. If the blood on the socks or other items shows no traces of that preservative, it would prove that the evidence could not have been tainted with that blood, Harmon said.

Harmon added that prosecutors would be willing to submit the samples to a mutually agreeable laboratory--or to one that Ito might suggest. Prosecutors, Harmon said, are prepared to abide by whatever results such a laboratory reports with regard to the presence of any preservative if the defense will join in that pledge.

Robert Blaiser, a DNA expert for the defense, refused, saying the Simpson team instead wants to test the evidence itself and draw its own conclusions. Legal experts said that defense attorneys could not agree in advance to the admission of evidence that might harm their client.

Ito asked prosecutors for an update Monday on how the blood might be tested and where.

Over the past week 10 witnesses have testified as part of the prosecution’s domestic violence case against Simpson but none with the dramatic impact of Brown’s appearance late Friday.

Earlier in the day, a police officer described the scene at Nicole Simpson’s house after a 1993 incident in which she called for help after Simpson came to her house yelling and cursing. Sgt. Robert Lerner said he and four other police officers spent more than an hour calming O.J. Simpson. But Lerner added that Simpson never struck his ex-wife during that altercation and was not arrested.

Lerner was followed on the stand by the first two witnesses to hint at the notion that Simpson stalked his ex-wife. That testimony was disjointed and confusing, however, as the two of them--a husband and wife who lived next door to Nicole Simpson in 1992--seemed to have difficulty abiding by the judge’s instruction that they confine their answers to the specific questions posed to them.

Nevertheless, one of those witnesses offered new details about arguments between O.J. Simpson and his ex-wife. Catherine Boe testified that Nicole Simpson would not let her ex-husband into her house on one occasion.

Another time, O.J. Simpson seemed angry about Nicole Simpson being involved with another man, she said, even though the Simpsons already were separated. When Shapiro suggested that perhaps Simpson had worried about his ex-wife and her new boyfriend having sex near Simpson’s children, Boe disagreed.

“I don’t think he was concerned about whether it was in the presence of the children,” she said. “I think he was concerned about whether it was his wife.”

Prosecutors had hoped to show that Simpson was stalking his wife during the early months of 1992, and asked Boe and her husband, Carl Colby, about an evening when they called police after spying a suspicious man outside. That man turned out to be Simpson, but Boe and Colby both conceded that they could not be sure why he was there or even whether Nicole Simpson was home while he was outside.

During his testimony, Colby said he called police in part because he found it odd that a person of Simpson’s “description” was in the neighborhood at that hour. As he said that, a black alternate juror rolled his eyes toward the ceiling, and another alternate, also black, chuckled to herself.

“What the prosecution described as O.J. stalking Nicole might be interpreted by some African American jurors as a classic example of white middle class people overreacting to the presence of an unknown black man in their neighborhood at night,” said UCLA law professor Peter Arenella.

If their testimony sputtered, however, Brown’s exploded.

She is the only person to take the stand thus far with an undisputed relationship both to Nicole and O.J. Simpson, and her account offered jurors their first glimpse inside that tempestuous relationship. That is central to the prosecutors’ theory of the June 12 murders, which they contend were committed as the final attempt by O.J. Simpson to control his ex-wife after years of manipulation and abuse.

But while her testimony delivers emotional and substantive weight to the prosecution case, Brown also offers the defense ample material with which to challenge her credibility. Since the murders, she has given many interviews to newspapers, magazines and television reporters, and in sessions immediately after the murders, she denied that her sister was a battered woman.

She told the Los Angeles Times that Nicole Simpson would never have tolerated abuse. She said the same thing to the New York Times and others. “If she was beaten up, she wouldn’t have stayed with him,” Brown said of her sister in one interview with the New York Times less than two weeks after the murders. “That wasn’t her. Everybody knows about 1989. Does anybody know about any other time?”

In fact, Brown now says that she herself knew of other instances, including the two she described on the stand Friday. When it is their turn to question her, defense attorneys can be expected to explore that and other contradictions between her testimony and the comments she made in interviews immediately after the murders.

Brown also may face questioning about her apparent bias against Simpson. At one point during her testimony Friday, she described Simpson as having a “huge ego.” Judge Ito ordered that remark stricken from the record.

In addition, members of Simpson’s family said they were at the Simpson house during the fight that Brown described on the stand and expect to offer their version as witnesses for the defense.

Even as court recessed for the weekend, other developments continued to crop up. A spokeswoman for the district attorney’s office said Deputy Dist. Atty. William Hodgman, who was sidelined last week with chest pains, is expected to rejoin the prosecution team the week of Feb. 16.

Meanwhile, Pete Peterson, a Colorado private investigator hired by a group calling itself Friends of Nicole, said Friday that he has uncovered a witness who maintains that O.J. Simpson stalked Ron Goldman in 1992.

Prosecutors have revealed only one instance in which they place Simpson and Goldman at the same location before the June 12 murders. Ito gave them permission to tell the jury about an incident last year in which Simpson allegedly saw his ex-wife having coffee with Goldman and another man.

“This incident is relevant as evidence connecting Brown Simpson and Goldman with defendant, and as evidence of jealousy and motive,” Ito ruled in allowing the jury to hear about that incident.

But Peterson said a new witness will provide details of other incidents in which Simpson allegedly spied on Goldman. Peterson declined to be more specific but has scheduled a press conference for today to unveil the latest allegations.

Prosecutors do not believe that Goldman was the intended target of the June 12 killings. Rather, they have maintained that Simpson came to his ex-wife’s condominium to kill her and that he murdered Goldman when the young man arrived to return a pair of eyeglasses to Nicole Simpson and was mistaken as a suitor.

Simpson’s attorneys have said that at the time of the slayings he was home chipping golf balls in his back yard and perhaps then dozing before a limousine arrived to take him to the airport.

Times staff writer Ralph Frammolino contributed to this story.