HOUSTON (Reuters) - Former Enron Corp. Chairman and Chief Executive Kenneth Lay on Thursday is to surrender to face criminal charges related to his leadership of the energy giant, which fell from Wall Street's loftiest heights into corporate exile and bankruptcy.

Lay, who has steadfastly denied all wrongdoing, said in a statement on Wednesday that he had been indicted and would turn himself in on Thursday.

Whether ultimately found guilty or exonerated, Lay's indictment is an ignominious turn for a man who once counted presidents among his friends and was the toast of corporate America.

The 62-year-old is to follow a well-worn path for former Enron executives: surrender to the FBI and then make his initial appearance before a federal magistrate judge.

Sources on Wednesday said a federal grand jury returned a sealed indictment with undisclosed criminal charges for Lay's actions before the company fell into bankruptcy in December 2001.

"I have been advised that I have been indicted. I will surrender in the morning," Lay said. "I have done nothing wrong, and the indictment is not justified."

As has been the pattern with most of the 21 other ex-Enron employees charged with crimes, the U.S. Securities and Exchange Commission is also expected to file civil charges against him.

Houston-based Enron was the nation's seventh-largest publicly owned company when it spiraled into a then-record bankruptcy in the final months of 2001.

Disclosures that the company hid billions in debt and burnished its financial statements through the use of esoteric, off-the-books transactions prompted the swift failure.

Lay, once a leading U.S. industrialist and close friend of President Bush -- who called him "Kenny Boy" -- now faces felony charges stemming from the debacle.

As Enron steamed toward a certain end, Lay's appeals for help to top Bush administration officials, including Commerce Secretary Don Evans, were met with silence.

The charges come 2-1/2 years after the U.S. Justice Department's Enron Task Force began an investigation which has slowly climbed the corporate ladder toward the executive suite.

Former Chief Financial Officer Andrew Fastow pleaded guilty in January in exchange for a 10-year prison term and is cooperating with prosecutors who were aiming higher.

He helped prosecutors bring charges against Lay's hand-picked successor, Jeff Skilling, who unexpectedly quit in August 2001, six months after becoming CEO.

He and former chief accountant Rick Causey were charged together and have both pleaded not guilty to more than three dozen counts of insider trading, fraud and lying on Enron financial statements. Observers have speculated Lay could face similar charges.

Enron's fall touched off investigations that uncovered widespread financial fraud in corporate America and a host of other corporate failures. The company, which had once been seen as an innovative vanguard, suddenly became the symbol of corporate misconduct.

Lay, as head of then Houston Natural Gas, led a 1985 merger that formed the modern Enron. He became an aggressive political player who lobbied politicians like Bush and his father, former President George H.W. Bush, to deregulate natural gas markets.

Generous campaign donations -- at one time he was the current President Bush's top contributor -- gave him access to the halls of power. His name was even bandied about as a potential energy secretary when the current president was assembling his cabinet.

Lay was Enron's chief executive for most of the company's history, ceding those duties to Skilling from February 2001 until his successor abruptly quit the following August.