NEW YORK (CNN/Money) - Martha Stewart won a round in court Friday as a judge ruled that prosecutors cannot call expert witnesses to testify that she duped investors into buying stock in her company by making false statements.

Judge Miriam Goldman Cedarbaum ruled that the government cannot ask Wall Street analysts if their ratings of Martha Stewart Living Omnimedia stock were influenced by Stewart's statements that she did nothing wrong in selling her ImClone Systems Inc. stock in late December 2001.

Stewart's assistant, Ann Armstrong, provides damaging testimony. CNNfn's Allan Chernoff reports. Play video (Real or Windows Media)

The statements are essential to the government's assertion that Stewart tried to influence the price of her own company's stock with her denials of wrongdoing in the case.

After the judge's decision, Stewart's lead attorney, Robert Morvillo, told CNNfn that the ruling doesn't "knock out securities fraud in and of itself." Asked if the ruling makes the government's securities fraud charge tougher to prove, he said, "Who knows?"

The ruling came before the jury entered the courtroom for the tenth day of testimony, with FBI agent Katherine Farmer answering more questions about the reliability of her notes on regulators' meetings with Stewart.

Under cross-examination by a lawyer for Stewart, the FBI agent testified that Stewart said she called ImClone founder Sam Waksal only after trying to sell her ImClone stock on Dec. 27, 2001.

Stewart also told the government that her friend Heidi DeLuca was aware of the agreement she had with her broker at Merrill Lynch, Peter Bacanovic, to sell shares at $60, Farmer told the court.

Farmer was the only one on the government's side to take notes during interviews with Stewart, conducted jointly with officials from the Securities and Exchange Commission and the U.S. Attorney's Office.

Michael Ryan, a special agent for the FBI, took the stand later Friday but his testimony was cut short as the prosecution and the defense sparred over which telephone records could be entered as evidence. The defense asked for more time to review the documents, and the judge agreed, adjourning court in mid-afternoon.

Ryan is expected to take the stand when the trial resumes Tuesday. Monday is President's Day.

Stewart is accused of lying to investigators about the reason for her stock sale and trying to prop up the price of Martha Stewart Living stock by not telling the truth.

The government says Stewart sold because of an inside tip -- passed from Bacanovic through his assistant at the time, Douglas Faneuil, to Stewart -- that ImClone founder Sam Waksal was trying to sell on Dec. 27, 2001. Stewart and Bacanovic say they had a long-standing pact to sell ImClone stock if the shares fell below $60.

On Wednesday, the ninth day of the trial, Stewart's lawyer asked for a mistrial, but the federal judge overseeing the case denied the motion.

Morvillo said the government's charges, which include reference to a "secret tip," were really about insider trading, meaning he should be allowed to try to exonerate Stewart by showing such trading never occurred.

"I have the right to prove a lack of motive by proving there was no insider trading," Morvillo told the court.

"You're saying this trial is being transferred to an insider trading trial?" Judge Cedarbaum asked. "You read a secret tip as insider trading. That's not a ground for dismissing the indictment," she said, denying the mistrial request.

The surprise move by Morvillo came right before an SEC investigator took the stand for a second day to discuss Stewart's first meeting with regulators on Feb. 4, 2002.

Helene Glotzer, assistant regional director at the agency, said Tuesday that Stewart claimed she had no recollection of being told Waksal was selling his stock before she sold.

In the February meeting, Stewart said she and Bacanovic had a prior agreement to sell her 3,928 shares of ImClone when the stock fell to $60, Glotzer told the court.

Related Links • Stewart's Employment Agreement at Martha Stewart Living Omnimedia Inc. • Court Ruling Dismissing 'Selective Prosecution' Defense • Superseding Indictment (U.S. v. Stewart and Bacanovic)

The SEC investigator said that when she asked Stewart about a telephone message from Bacanovic, Stewart said she didn't know whether the message had been recorded in the computerized log.

When Morvillo cross-examined Glotzer on Wednesday, Glotzer said Dave Marcus, a lawyer at Merrill Lynch, told her that Stewart's stock trade had nothing to do with Waksal's.

Glotzer testified that Marcus said Stewart's ImClone sale was one of many trades she made in the final week of December 2001.

And, in an attempt to discredit the government's witness as biased, Stewart's attorney asked Glotzer if it's her hope that the government wins the case.

"Yes, I believe in the case," Glotzer answered.

The prosecution played an audio tape after Glotzer's testimony Wednesday, detailing an interview the SEC conducted with Bacanovic back in 2003 about Stewart's stock sale.

The former Merrill Lynch broker told regulators on the tape that he couldn't recall who -- either himself or Faneuil -- had placed a call to Stewart, but he said a message was left with her assistant, Ann Armstrong, to ask Stewart to return the call.

When Stewart did return the call, Faneuil gave her the share price of ImClone, and Stewart asked to sell her remaining shares based on that stock price given by his assistant, Bacanovic told the SEC on the tape.

"I do not discuss my clients affairs with other clients," Bacanovic said on the tape, referring to the SEC's accusation that he had shared the information about Waksal's ImClone stock sale to Stewart. "I did not get to be a first vice president at Merrill Lynch by discussing other people's business," he added.

Armstrong testified Tuesday that the home decor expert personally changed a Dec. 27, 2001, phone message from Bacanovic telling her that ImClone stock would start falling, but then changed the message back.

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Federal prosecutors hope Armstrong's statements will show that Stewart sought to cover up details about her ImClone trade.

Faneuil, the government's star witness, ended his testimony in the obstruction of justice trial Monday. Faneuil has pleaded guilty to a misdemeanor for his part in the scheme and agreed to testify about Stewart's sale, and much of the government's case will hinge on whether jurors believe him.

Over four days on the witness stand Faneuil has told jurors repeatedly that he gave Stewart the tip that Waksal and members of his family were trying to sell.

But Monday he conceded that he never discussed a cover-up with Stewart and she never encouraged him to lie about their conversation.

Related link • Stewart's message log

Stewart, the lifestyle expert who founded Martha Stewart Living Omnimedia (MSO: Research, Estimates), faces up to 30 years in prison while Bacanovic could be sentenced to 25 years if convicted on all counts, according to the U.S. Attorney's office.

Waksal is serving a seven-year prison term after pleading guilty to charges of trying to sell ImClone (IMCL: Research, Estimates) stock a day before a negative announcement started the shares tumbling.  

-- with CNNfn's Kelly Marshall and staff and wire reports