Federal prosecutors are investigating a stock sale by the wife of former Enron Corp. chairman Kenneth L. Lay just days before the Houston energy trader filed for bankruptcy protection in late 2001, according to lawyers involved in the probe.

At the center of the new inquiry is Linda P. Lay's sale of 500,000 Enron shares on behalf of the couple's family foundation on Nov. 28, 2001. The sales netted $1.2 million, which was used to cover pledges the foundation had made to local charities, said Michael Ramsey, the family's lawyer.

He said prosecutors are examining whether Linda Lay traded on inside information -- namely, that Enron's merger with rival Dynegy Inc. was collapsing and that the company was about to declare bankruptcy and make its stock nearly worthless.

The investigation of Linda Lay, reported by the New York Times on Wednesday, ratchets up pressure on her husband, who was indicted earlier this year on conspiracy, bank fraud and false statements charges.

Exerting pressure on family members of a prime government target is not unusual in major tax investigations and in high-profile white-collar fraud cases, legal experts said.

The Justice Department's Enron Task Force employed a similar tactic last year against the company's former finance chief, Andrew S. Fastow. Fastow eventually pleaded guilty to two fraud charges and agreed to cooperate with the government, but only after his wife, Lea W. Fastow, had been indicted on tax charges. Lea Fastow is serving a one-year prison sentence.

Andrew Weissmann, director of the task force, declined to comment.

Ramsey, who represents both Linda and Kenneth Lay, blasted investigators for trying to "intimidate" his clients.

"This trade is as clean as can possibly be," Ramsey said. He added that neither of the Lays personally profited from the stock sale, which was made on the same day a credit rating agency downgraded Enron's debt.

"This only digs him in deeper and makes him more angry inside," Ramsey said of Kenneth Lay. "This is a nothing investigation. It's reaching over his shoulder to strike at his wife."

Ramsey said he had not received formal notification that Linda Lay is the target of a grand jury investigation, a move that would indicate the government is likely to seek a criminal indictment.

Meanwhile, FBI, NASD, and Securities and Exchange Commission staffers continue to investigate stock sales and possible securities law violations by middle managers at Enron, according to lawyers involved in the probe. Federal prosecutors also are examining the activities of former employees in the company's finance and international units.

More than 30 people have been criminally charged for their dealings with Enron, including former chief executive Jeffrey K. Skilling and accounting chief Richard A. Causey, who have pleaded not guilty and await trial alongside Kenneth Lay.

Linda P. Lay and her husband, former Enron chairman Kenneth L. Lay, did not personally profit from the stock sale, their lawyer said.