When they broke rules before, the O.J. Simpson judge snapped at prosecutors. He fined one of them. He ordered them to put witnesses on hold. But he never barred them from presenting evidence.

Until now.Superior Court Judge Lance Ito imposed the trial's harshest penalty yet on prosecutors for playing dirty, preventing them from presenting a five-page report that links fibers on murder evidence to the carpet in Simpson's Ford Bronco.

Following a passionate hearing Thursday outside the jury's presence, Ito said prosecutors had violated state rules requiring both sides to trade evidence in advance.

Legal analysts said the ruling was a major - but not lethal - setback for the prosecution at a delicate time. After five months of testimony, prosecutors expect to wrap up their case next week with more testimony from FBI hair and fiber expert Douglas Deedrick, followed by the final witness: Nicole Brown Simpson's mother, Juditha Brown

Prosecutor Marcia Clark said she would question Brown about eyeglasses she left at Mezzaluna restaurant the night of the killings and a call to her daughter shortly before her death.

Ronald Goldman, a waiter at Mezzaluna, went to Ms. Simpson's condominium to return the glasses and was murdered alongside his friend on June 12, 1994.

Deedrick returns to court today for more testimony.

In what the judge called "compelling" evidence, Deedrick's FBI report showed that only Broncos made in 1993 and 1994 had the kind of carpet containing the fibers found on a knit cap near the bodies and a bloody glove behind Simpson's house. Simpson's Bronco is a 1994 model.

"You hate this close to the end of the (prosecution) case to lose any evidence, especially in a circumstantial evidence case," said Loyola University law professor Laurie Levenson. "What they lose is the ability to tell the jurors how rare the match is. It's a partial loss."

Pepperdine University law professor Timothy Perrin said Deedrick would only be able to testify that the evidence fibers and the fibers from Simpson's Bronco are similar, without putting the issue into context.

"This evidence is less compelling, less powerful," Perrin said. "The fibers match . . . but they're not going to be able to say they came from a '93 or '94 Bronco, which specifically points the finger at O.J. Simpson."

The order barring the evidence was Ito's most severe sanction of the trial for discovery violations.

In the past, Ito has ordered prosecutors to delay some witnesses until the end of the trial because their identities had not been disclosed to defense lawyers. When the defense failed to share information about witnesses, the judge admonished jurors that Johnnie Cochran Jr. had failed to abide by discovery orders. But Ito had never precluded any evidence from the case.

In Thursday's hearing, Clark admitted not telling defense lawyers that Deedrick obtained data from a carpet manufacturer. But Clark insisted she didn't know about Deedrick's report until Wednesday night, when he reluctantly disclosed it to the defense on orders of the judge.