Martha Stewart asked a federal judge Thursday to throw out her criminal conviction, contending that the alleged perjury of a government witness "fatally undermined" her right to a fair trial.

The multimillionaire businesswoman and her former broker, Peter E. Bacanovic, were convicted in March of conspiracy, obstruction of justice and lying to federal investigators about her December 2001 sale of ImClone Systems Inc. stock.

Their sentencing was delayed until July 8 after the arrest last month of Secret Service ink examiner Larry F. Stewart , no relation to Martha Stewart, on charges that he committed perjury at their trial by allegedly exaggerating his role in testing the ink on a worksheet created by Bacanovic.

Now lawyers for Martha Stewart and Bacanovic, who filed his own motion Thursday, are arguing that the ink examiner's testimony amounted to "government misconduct" because prosecutors should have known he was lying on the stand.

Yesterday's requests are the defendants' second attempt to get U.S. District Judge Miriam Goldman Cedarbaum to order a new trial. Cedarbaum rejected the previous motion, which alleged that a juror, Chappell Hartridge, was biased against Stewart and failed to disclose earlier brushes with the legal system.

"No conviction should be premised on the perjured testimony of any government official," Stewart's lawyers, Robert G. Morvillo and John J. Tigue, said in a written statement. "How many demonstrations of perjury are necessary before the government will act to correct the miscarriage of justice which resulted from all of the misconduct?"

Bacanovic's spokesman, Lou Colasuonno, said, "When a key member of the prosecution team lies, the verdict cannot stand."

A spokeswoman for U.S. Attorney David N. Kelley, who is prosecuting both the Larry Stewart and Martha Stewart cases, declined to comment. Kelley said upon Larry Stewart's arrest last month that his office had just learned of the alleged perjury and that there was nothing wrong with the underlying ink analysis.

Prosecutors argued at trial that the lab work showed that Bacanovic had doctored the worksheet to support his and Martha Stewart's contention that they had agreed to sell her ImClone shares if their price fell to $60. They said Stewart sold after Bacanovic's assistant improperly told her that ImClone's founder was trying to dump his shares in the company.

The question of what prosecutors knew about Larry Stewart's testimony is crucial to the outcome of Martha Stewart's case, legal analysts said.

According to legal precedents, if prosecutors knew or should have known Larry Stewart's testimony was false, Martha Stewart's lawyers have to prove only that his testimony could have affected the jury's verdict. If prosecutors were fooled with the defense, she would have to show that she would not have been convicted without the perjured testimony.

"Knowing use of perjury is much more egregious a problem than just the fact that a government witness lied," said former federal prosecutor Mark J. Biros, who now heads the D.C. office of the law firm Proskauer Rose LLP.

Morvillo's filing Thursday did not accuse prosecutors of knowing about the alleged perjury, but it noted that Larry Stewart met repeatedly with prosecutors in preparation for his testimony and that several of his colleagues from the laboratory were present while he was on the stand.

The colleagues' "silence is scandalous and not the way we expect the government to conduct itself," Morvillo and Tigue said in their statement. They asked the judge to hold a hearing on exactly what different members of the prosecution team knew.

Martha Stewart's motion also argued that Larry Stewart's allegedly false claim that he -- rather than a subordinate -- had tested the worksheet deprived her of her constitutional right to confront the witnesses against her. She should, the lawyers wrote, have been allowed to cross-examine the lower-level employee who did the testing.

It is not known how important Larry Stewart's testimony was to the jurors who convicted Stewart and Bacanovic. The jury acquitted Bacanovic of making a false document and declined to convict either defendant of lying about the alleged arrangement to sell when the stock reached $60.

But Martha Stewart's motion yesterday called the testimony "pivotal scientific corroboration to a prosecution based primarily on circumstantial evidence and one that otherwise lacked tapes, transcripts, or other unassailable evidence of wrongdoing." The defense team also noted that testimony about the ink on the worksheet took three days, longer than any other subject except the testimony of Bacanovic's assistant, Douglas Faneuil.