Attorneys trying to overturn Martha Stewart’s conviction in a stock trading trial accused the government yesterday of improperly withholding evidence that “could have led to an acquittal.”

The accusation, contained in a letter to federal prosecutors and the judge who oversaw the trial, came one day before Stewart’s deadline to report to a federal prison in West Virginia to begin serving a five-month sentence.

Stewart’s attorneys said prosecutors should have provided the defense with documents that emerged as evidence during the recent perjury trial of ink expert Larry Stewart, who testified against Martha Stewart.

Among the documents is a 2002 memo written by a Secret Service scientist who tested the ink on a worksheet of Martha Stewart’s stock holdings – a key piece of evidence against the homemaking maven and her former stockbroker.

In the memo, scientist Susan Fortunato wrote that ink in a notation of “(at)60” next to a listing for ImClone Systems Inc. stock was different from “all” other inks on the worksheet.

That contention bolstered the government’s case that the broker, Peter Bacanovic, had doctored the worksheet by adding the “(at)60” notation to support a cover story for why Martha Stewart sold ImClone stock.

In fact, Ms. Fortunato had not tested all the ink on the worksheet. She failed to test a dash mark that appeared next to another stock listing – an omission Martha Stewart’s lawyers say “sabotaged” the testing. “That could have led to an acquittal – if the government had complied with its … obligations and the jury had been aware of the memo,” the letter from Stewart’s lawyers said.

Defense attorneys said they had made repeated unsuccessful requests to federal prosecutors to obtain the full laboratory file for the document testing, including the 2002 memo.

“The government’s crime lab sabotaged the critical testing in an effort to secure her indictment and conviction,” the letter said. “That revelation to the jury could have easily led it to conclude that the government overreached in prosecuting Ms. Stewart.”

Federal prosecutors in Manhattan had no comment, spokeswoman Megan Gaffney said.

Larry Stewart was acquitted earlier this week of perjury charges. Federal prosecutors had accused him of lying on the witness stand at Martha Stewart’s trial, exaggerating the role he played in the testing of the worksheet.