Former Enron accounting chief Richard Causey pleaded guilty to a federal securities fraud charge yesterday and agreed to cooperate with prosecutors, a move expected to strengthen the impending prosecution of Enron's former top two executives.

Causey entered the plea in Houston federal court 20 days before he was to stand trial with former Enron chairman Kenneth Lay and former CEO Jeffrey Skilling for alleged schemes that led to the firm's Chapter 11 bankruptcy filing in 2001.

In a written statement filed with the plea, Causey, 45, said he conspired with other top company executives "in efforts to use Enron's public filings and public statements to mislead the investing public" about the firm's true financial performance.

After accepting the plea from Causey, the 16th cooperating figure in the case, U.S. District Judge Sim Lake delayed the trial's start to Jan. 30. That gave lawyers for Lay and Skilling two extra weeks to prepare for the likelihood that Causey, once part of a united defense front, would be a key prosecution witness.

Causey is to serve seven years in federal prison and forfeit $1.25 million under the plea deal. The agreement also says prosecutors might ask that his term be cut to five years if they feel he "provides truthful, complete and accurate information."

Causey's lawyer, Reid Weingarten, said his client entered a guilty plea, "not a cooperation agreement."

"To the extent that he has any involvement in any upcoming legal proceedings, he will do one thing: He will tell the truth, because that is who he is, that is what he should do," he told reporters outside court.

Skilling's lawyer, Daniel Petrocelli, said testimony by Causey would not damage the defense because, "He has professed all along that Enron's accounting was proper, and I don't expect that to change."

Several legal experts nonetheless called the development a potentially critical blow for the defense.

His cooperation should be "enormously helpful" to prosecutors, "because he was Enron's money man, and he dealt with Lay and Skilling face to face," said Robert Mintz, a former federal prosecutor at the law firm of McCarter & English.