NEW YORK (CNN/Money) - Martha Stewart asked a federal judge Thursday for a new trial, citing charges that a key government witness lied on the stand.

The request comes about a month before Stewart and her ex-broker at Merrill Lynch are to be sentenced for lying about a well-timed stock sale by Stewart in late 2001.

The motion follows perjury charges filed late last month against Larry Stewart, a U.S. Secret Service laboratory director, accusing him of falsely testifying that he carried out tests on a key document in the trial. Martha and Larry Stewart are not related.

In their motion, Martha Stewart's lawyers called it "sadly ironic" that the recent perjury charges against Larry Stewart prompted their request.

They noted this was the second time they've asked for a new trial which, they argue, "conclusively demonstrates that the trial process was marred by dishonesty and perjury."

In their earlier motion, defense lawyers argued that one of the jurors, Chappell Hartridge, lied about his past during jury selection.

Judge Miriam Goldman Cedarbaum denied that request in early May.

The new motion argues that Larry Stewart's testimony "was at the core" of the government's case and the "focal point" of its preparation for trial.

In a statement posted on www.marthatalks.com late Thursday, Martha Stewart's lawyers claimed that several Secret Service officials who attended the trial were aware of Larry Stewart's alleged perjury "but did nothing to bring it to the attention of the court."

Stewart leaves court with her lawyer in March.

In their filing, Martha Stewart's lawyers said they were not accusing prosecutors of knowing that Larry Stewart was allegedly lying on the stand. But they requested a court hearing to find out which "members of the prosecution team" knew about the alleged lies.

Prosecutors declined comment on the new filing. In a news conference soon after filing perjury charges last month against Larry Stewart, U.S. Attorney David Kelley said he was confident that the case would have "no impact" on Martha Stewart's conviction.

The founder of Martha Stewart Living Omnimedia (MSO: down $0.12 to $9.33, Research, Estimates) and Peter Bacanovic, her former broker, were convicted in March of lying about Stewart's sale of nearly 4,000 shares of ImClone Systems stock in December 2001.

Just how central Larry Stewart's testimony was in the case is a matter of considerable debate among legal experts.

During the six-week trial, Larry Stewart testified about pen ink that seemed to help prove a key point in the government's case against Martha and Bacanovic: that the duo tried to cover their tracks in the weeks after Stewart sold her ImClone stock, allegedly after receiving an inside tip.

Larry Stewart testified that a notation Bacanovic had made on a worksheet -- "@60" -- was made with ink different than the other ink on the sheet. The testimony was important because Stewart and Bacanovic claimed they had a pre-existing agreement to sell her ImClone stock if the price dropped below $60 a share.

Some criminal defense lawyers have argued that Larry Stewart's testimony was not sufficiently damaging to Martha Stewart or Bacanovic. They noted that the jury exonerated Bacanovic on a separate charge that he doctored the worksheet as part of the duo's coverup.

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But Bradford Lewis, a former federal prosecutor who read Martha Stewart's motion, said her lawyers raised three good points. One is that Bacanovic's worksheet was important to a case that was largely based on circumstantial evidence.

Another point is that the dispute over the "@60" mark was part of the government's overall conspiracy case against Martha Stewart, not just part of its falsifying document charge against Bacanovic.

And, finally, Lewis said, government lawyers can't now distance themselves from Larry Stewart when they effectively admitted in their perjury complaint against him that he was important to their case.

"Her lawyers are trying to point out that the government is trying to have it both ways, and I think they do a good job of that," said Lewis, now a partner in Fenwick & West in Palo Alto, Calif.

Judges are often reluctant to overturn jury verdicts and start over with a new trial. If Cedarbaum rejects the latest motion for a new trial, the case is expected to move to the court of appeals.

Larry Stewart was also indicted by a grand jury Wednesday on two counts of committing perjury. He is scheduled to appear in court to enter a plea next week. His lawyer, Judith Wheat, said Thursday that he will plead not guilty to the charges.

"He has been a dedicated public servant for 25 years," said Wheat. "To our knowledge his integrity has never been called into question before. He stands behind the work he did in the case and the testimony he gave in what is, by all accounts, a very heated trial situation."