Martha Stewart (search)  asked a judge Thursday for a new trial, citing allegations that a Secret Service ink expert who testified against her lied repeatedly on the stand.

The request, considered a long shot by legal experts, came four weeks before Stewart and former stockbroker Peter Bacanovic (search ) are to be sentenced for lying about a well-timed stock sale by the celebrity homemaker in 2001.

She argued that her conviction was tainted by perjury charges brought recently against Larry Stewart, a Secret Service (search ) laboratory director who was called as an expert witness at her trial in February.

Prosecutors say Larry Stewart lied on the stand about the role he played in ink-analysis tests conducted on a worksheet prepared by Bacanovic.

In court papers, Martha Stewart's lawyers called Larry Stewart's testimony "pivotal scientific corroboration to a prosecution based primarily on circumstantial evidence."

"Simply stated, a verdict that rests upon such a corroded foundation cannot stand," the the lawyers said.

They also said that several other Secret Service officials were in court, monitoring the trial, and were aware of the alleged perjury but did not say anything about it.

"Their silence is scandalous and not the way we expect the government to conduct itself," Stewart's lawyers, Robert Morvillo and John T. Tigue, said in a statement.

Prosecutors did not immediately respond to a request for comment. But the government has insisted the perjury charges do not undermine the conviction. Bacanovic was acquitted on a charge of falsifying a document -- the subject at the heart of Larry Stewart's testimony.

Legal experts have noted that defense lawyers face a high hurdle in arguing for a new trial based on perjury charges against a prosecution witness.

"This is a tough argument for the defense to make," said Mark Zauderer, a lawyer in private practice. "They have to show that unless the government was deliberately involved in the false testimony -- which is not the case here -- the result would have been different in the trial had the perjury not occurred."

Larry Stewart was charged with perjury in May. He is due in court June 16 to enter a plea.

Martha Stewart and Bacanovic were convicted March 5 of lying about why Stewart sold 3,928 shares of ImClone Systems (IMCL)  just before it plunged on a negative government report about an ImClone cancer drug.

Prosecutors claimed she dumped her stock after her broker tipped her off that ImClone founder Sam Waksal was unloading his own holdings. But she and her broker claimed that they had a standing agreement to sell when the stock dropped below $60.

The government called Larry Stewart at the trial to discuss a worksheet that prosecutors said Bacanovic doctored by adding a notation of "(at)60." Larry Stewart testified that the ink used to make the notation was different from the ink used on other parts of the worksheet.

Defense lawyers never contested that point.

Later, the witness was charged with lying in saying he performed some of the ink analysis himself.

Stewart made her first bid for a new trial on May 5. She argued a juror had lied on his questionnaire in failing to mention a prior arrest on assault charges, among other things.

But U.S. District Judge Miriam Goldman Cedarbaum ruled it was not clear that the juror had lied at all -- or that lawyers would have kept him off the case had they known about his background.

Stewart and Bacanovic are scheduled to be sentenced July 8. Each is likely to receive a 10- to 16-month prison sentence.