NEW YORK (AP) — A federal judge in the Martha Stewart trial on Friday ruled out expert testimony that had been sought by prosecutors, hurting their effort to prove she committed securities fraud.

The testimony barred by U.S. District Judge Miriam Goldman Cedarbaum would have discussed how investors might have reacted to Stewart's public statements about her ImClone Systems sale.

The securities fraud count — the most serious against the homemaking entrepreneur — accuses Stewart of propping up the stock price of her own company, Martha Stewart Living Omnimedia, by claiming in 2002 that her ImClone sale was proper and that she was cooperating with authorities.

Conviction on the securities fraud count would carry a 10-year prison term. Each of the other four counts against Stewart would carry five years.

Cedarbaum's ruling granted a motion by Stewart over statements she made in 2002, blocking testimony on "whether a reasonable investor would have considered the statements important in making an investment decision," the judge said.

The order came as the 10th day of testimony got under way at the trial of Stewart and ex-stockbroker Peter Bacanovic.

They are accused of lying to investigators about why Stewart sold 3,928 shares of ImClone on Dec. 27, 2001.

The pair claim they had a pre-existing understanding to sell the stock when it fell to $60 per share. But the government says Stewart was tipped that ImClone CEO Sam Waksal was trying to dump his own shares.

ImClone shares tumbled after the government announced the next day that it was rejecting the company's application for approval of the cancer drug Erbitux.

The Food and Drug Administration finally approved the drug Thursday, sending ImClone shares sharply higher in early Friday trading.

Stewart's lawyers spent Friday morning attacking the credibility of an FBI special agent whose notes are the only government record of Stewart's two interviews with investigators in 2002.

One of the charges against Stewart is that she lied when she said in one interview that she did not recall whether her office kept a log of a message left by Bacanovic on the day of the stock sale.

But FBI special agent Catherine Farmer testified Friday she had no notes of Stewart specifically saying she did not remember such a log. Farmer apparently wrote only in a report she prepared after the interview that Stewart said she could not recall.

"And you were the only person taking notes for the United States government that day, right?" Stewart lawyer John Tigue asked.

"Yes," Farmer replied.

Stewart's assistant has testified Stewart personally altered the log of the Bacanovic message, then ordered that it be restored.