A federal grand jury in Houston issued a sealed indictment against former Enron Corp. chief executive Kenneth L. Lay yesterday, and prosecutors are set to make the criminal charges public today.

Lay, 62, who has been under intense scrutiny since he presided over Enron's collapse in late 2001, issued a statement after news reports of the charges. "I have been advised that I have been indicted," he said. "I have done nothing wrong and the indictment is not justified."

The charges against Lay remained under seal yesterday, but other former leaders at the company have been accused of fraud, conspiracy and insider-trading offenses.

In recent months, the grand jury has heard evidence from a series of former employees who said they alerted Lay to mounting financial problems in the months before the company disclosed phony earnings and billions in hidden debt. Lay, Enron's founder and longtime chairman, was replaced as chief executive for six months ending in August 2001 by Jeffrey K. Skilling.

The Lay indictment is a major development in the government's most prominent investigation into corporate fraud after the Internet bubble burst in 2000. Skilling, Lay's handpicked successor, was indicted earlier this year.

Lay said he will surrender to authorities this morning. He is expected to appear at a brief court proceeding before a magistrate judge in Houston later in the day.

The Securities and Exchange Commission will bring related civil charges against Lay, according to sources who spoke only on condition of anonymity because of the ongoing 21/2-year-old investigation.

Investigators have probed a series of optimistic statements Lay made to analysts and employees in the months before Enron's fall, which cost thousands of workers their jobs and retirement savings. Lay also sold millions of dollars of Enron stock back to the company between August and December 2001, using a revolving line of credit as an "ATM machine," in the words of one former board member.

Lay has strongly denied wrongdoing through his lawyer Michael Ramsey, who told The Washington Post last month that Lay had been duped by underlings and that he sold stock only to cover losses in volatile technology investments. Moreover, Ramsey said, Lay held on to a substantial amount of Enron shares as the stock price dropped, losing potential profit in the process.

"We are very conversant with all the facts and all the documents," Ramsey said June 19. "I've seen nothing that will support a prosecution."

Prosecutors, who are barred from talking about pending charges, declined to comment.

Skilling was indicted on 35 fraud and insider-trading charges in February. The government says Skilling presided over a wide-ranging conspiracy that employed accounting maneuvers, false statements and other methods to prop up Enron's stock price in the years before it collapsed.

Legal experts said the trial could be among the most complex business schemes ever to be presented to a jury. Unlike the case of former Enron finance chief Andrew S. Fastow, who allegedly pocketed more than $60 million in company money without the board's knowledge, many of the accounting and legal issues reviewed by Skilling and Lay were vetted by outside experts. That could make it more difficult for prosecutors to convince a jury that the executives acted with intent to defraud.

So far the Justice Department's Enron Task Force has charged 30 people connected to the company with conspiracy and other crimes. Eleven individuals have pleaded guilty or been found guilty after trial. Among prosecutors' key cooperating witnesses on the Enron case are Fastow, former treasurer Ben F. Glisan Jr. and former corporate secretary Paula H. Rieker. All three pleaded guilty.

During Enron's heyday, when the firm reported revenue that ranked it seventh on the Fortune 500 list of publicly traded companies, Lay traveled the world to meet with power brokers and charity leaders. And he cultivated close ties to the Bush administration. President Bush nicknamed him "Kenny Boy."

More than anyone else, Lay was responsible for creating a vast energy company with operations that spanned the globe. Now that empire is a shell of its former self. The turnaround experts at Enron's helm are negotiating to sell its biggest assets and to return to creditors about 20 cents on the dollar in cash and stock in an international enterprise. A federal judge in New York is considering a plan that would allow the company to emerge from bankruptcy protection.

Kenneth L. Lay founded Enron.