BALLSTON SPA — The Saratoga County Sheriff's Department arrested one of its own Wednesday after a woman accused a deputy of forcing her into a sexual act with him.

Donald A. Harder III, 28, of Hadley, was on duty and responding to a call to assist with a civil matter on Shields Road in Edinburg when he began chatting with a 27-year-old acquaintance at the scene, Sheriff James Bowen said. Bowen was not specific about the nature of the alleged sex act, but said the victim was in the passenger seat of Harder's patrol car when it occurred.

Harder was charged with committing a criminal sex act in the first degree. If convicted, he could face up to 25 years in prison. Harder was arraigned before Corinth Town Justice Ambrose Clothier and pleaded not guilty. He was sent to jail on $25,000 cash bail or a $50,000 bond. Wednesday afternoon, Bowen said Harder had not made bail. Harder has been suspended without pay until the matter is resolved.

Harder was hired in August 2006 and had served without incident until this matter, Bowen said. He is married and has three children.

"It tears my heart out," Bowen said at a news conference with District Attorney James Murphy at the county jail. "I feel bad for his wife, but we have jobs to do."

Bowen said the last time he had to arrest one of his own staff was several years ago, when a lieutenant was charged in a domestic violence case involving his wife. Bowen said the Harder case is worse.

Murphy said the State Police forensic unit was called in to examine Harder's patrol car for evidence. When the investigation is completed, the case will be presented to a grand jury, he said.

While forcible compulsion is part of the charge of criminal sex act, neither Murphy nor Bowen would specify what Harder did to coerce the victim.

"She felt she had to commit the act," Bowen said.

Harder's defense attorney, Todd Morrow of Corinth, could not be reached for comment.