WASHINGTON  For years, a Congressional hearing with Alan Greenspan was a marquee event. Lawmakers doted on him as an economic sage. Markets jumped up or down depending on what he said. Politicians in both parties wanted the maestro on their side.

But on Thursday, almost three years after stepping down as chairman of the Federal Reserve, a humbled Mr. Greenspan admitted that he had put too much faith in the self-correcting power of free markets and had failed to anticipate the self-destructive power of wanton mortgage lending.

“Those of us who have looked to the self-interest of lending institutions to protect shareholders’ equity, myself included, are in a state of shocked disbelief,” he told the House Committee on Oversight and Government Reform.

Now 82, Mr. Greenspan came in for one of the harshest grillings of his life, as Democratic lawmakers asked him time and again whether he had been wrong, why he had been wrong and whether he was sorry.