SAN FRANCISCO —  A San Francisco radio talk show host pleaded not guilty to child pornography charges after surrendering to authorities Thursday.

The specifics of the allegations against Bernie Ward, 56, remain under seal. A spokesman for the U.S. Attorney's office in San Francisco did not immediately return a call.

Ward, frequently called the "lion of the left" for his staunchly liberal views, hosts a nightly news talk program on KGO-AM 810 as well as a program called GodTalk on Sundays. He produced an award-winning series that explored allegations of financial and sexual misconduct in the Archdiocese of San Francisco, according to the KGO Web site.

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Ward also is a frequent political commentator on various national cable network news programs.

Ward's criminal attorney, Doron Weinberg, insists that his client was merely doing journalistic research when he accessed the child pornography.

"Bernie was in the process of writing a book about hypocrisy in America," Weinberg told The AP. "As part of it, for a few days in December of 2004, he accessed child pornography."

Since that time, Ward and his attorneys have tried to convince investigators that his efforts were done in the pursuit of journalism, Weinberg said.

A substitute host would take over Ward's radio shows beginning Thursday, said Jack Swanson, operations director at KGO. He declined to comment on the case.