NEW YORK (Reuters) - The former outside accountant for Bernard Madoff's firm pleaded guilty to fraud charges on Tuesday, but told a U.S. judge he did not know about the swindler's massive Ponzi scheme.

The judge ordered the former accountant, David Friehling, to remain free on bond of $2.5 million (1.5 million pounds) until he is sentenced next year.

"At no time was I aware that Mr Madoff was engaged in a Ponzi scheme," Friehling told U.S. District Judge Alvin Hellerstein in Manhattan federal court in pleading guilty to charges of securities fraud and several other crimes. "I never had contact with investors and never acted as a feeder to investors."

Madoff, 71, is serving a 150-year prison sentence after pleading guilty to the decades-long investment fraud of as much as $65 billion. A Ponzi scheme is one in which early investors are paid with the money of new clients.

(Reporting by Grant McCool; Editing by Tim Dobbyn)