SAN DIEGO (Reuters) - The former child actor who was the voice of Charlie Brown in the 1960s "Peanuts" animated television specials pleaded not guilty on Wednesday to charges he threatened his girlfriend and a surgeon who carried out her breast enhancement surgery.

Peter Robbins, 56, from Oceanside, California, pleaded not guilty in San Diego Superior Court to two counts of stalking and 10 counts of criminal threats. If convicted, he could face up to nine years in prison, Deputy District Attorney Elizabeth McClutchey said.

Robbins was arrested on Sunday on outstanding warrants by U.S. Customs officers at the San Ysidro port of entry as he returned to San Diego from Mexico. He remains in jail.

McClutchey said on December 31 Robbins threatened Dr. Lori Saltz, the plastic surgeon he paid to perform breast enhancement surgery on his girlfriend, Shawna Kern.

The prosecution also alleged Robbins left several threatening phone messages for Kern, saying in one, "You better hide Shawna, I'm coming for you ... and I'm going to kill you."

Robbins allegedly threatened to kill a police sergeant who arrested him on January 13 after he refused to pay a restaurant bill at the San Diego hotel where he was staying.

Robbins was released on $50,000 bond the following day and given a January 28 court date.

McClutchey urged Judge David Szumowski to keep Robbins' bail set at $550,000 because Kern and Saltz believed Robbins was a "desperate man" and "had nothing to lose."

Defense attorney Marc Kohnen said the bail was excessive because Robbins had no criminal record and had never been in trouble with the law.

Robbins was 9 years old in 1965 when he became the voice of the world-weary yet optimistic title character of "A Charlie Brown Christmas," the first of many animated TV specials based on the popular "Peanuts" comic strip by Charles Schulz.

With its jazz-inflected music score and a storyline involving Charlie Brown's search for the true meaning of Christmas in a season corrupted by commercialism, it became a holiday TV classic.

The actor went on to voice Charlie Brown in "It's the Great Pumpkin, Charlie Brown," "You're In Love, Charlie Brown" and "A Boy Named Charlie Brown," which aired in the 1960s. He was replaced in later versions of the animated specials.