Former Enron Corp. assistant treasurer Timothy Despain pleaded guilty yesterday to conspiracy to commit securities fraud and agreed to cooperate with federal prosecutors investigating the company.

Despain, who worked at Enron from January 1999 to May 2002, appeared before U.S. District Judge Ewing Werlein Jr. in Houston and said he helped manipulate the company's credit rating to make Enron stock and bonds more appealing to investors.

"I was directed by my superiors to engage in, and did engage in, conduct that I recognized was intended to manipulate fraudulently Enron's credit rating," Despain said in a written agreement filed with the court.

The maximum penalty for Depain's crime is five years in prison and a $250,000 fine. Prosecutors agreed to recommend a lesser sentence in return for Despain's cooperation with the Enron Task Force, which is building a case against former Enron chief executives Kenneth L. Lay and Jeffrey K. Skilling. Each man was indicted on fraud charges this year and pleaded not guilty.

Earlier yesterday, Despain appeared before U.S. Magistrate Judge Stephen W. Smith to hear the charges and waived his right to have a grand jury hear evidence in the case.

Leslie Ann Gerardo, Despain's lawyer, and prosecutor Sean M. Berkowitz declined to comment.

Despain worked at Halliburton Co. after leaving Enron. Halliburton spokeswoman Wendy Hall said he no longer works for the company and she declined to say what his position was or when he left.

In the cooperation agreement, the government said it wouldn't prosecute Despain for any "heretofore disclosed participation in criminal activity in which he engaged in his capacity as an officer or employee of Enron and Halliburton."

Bryan Sierra, a spokesman for the Justice Department in Washington, declined to comment on whether Despain will be asked about his work at Halliburton as part of the plea agreement.

Halliburton in under investigation concerning its business dealings in Iran and its U.S. government contracts for work in Iraq. The company in August agreed to pay $7.5 million to settle Securities and Exchange Commission allegations of misleading financial reports.

During his time at Enron, Despain was the go-between for senior managers and credit rating companies Standard & Poor's and Moody's Investors Service, which tracked Enron's debt and how much cash was generated. Maintaining investment-grade ratings were critical to Enron's ability to get loans from banks, prosecutors said.