A 28-year-old day camp counselor, described by a Howard County recreation official as an "exceptional" worker, has been charged with sexually assaulting a 5-year-old boy at a county-run day camp, police said today.

Thomas C. Ayres, who supervised 130 youngsters as a recreation leader at a Columbia day camp, was arrested and charged Monday with assaulting the child July 29 at Longfellow Elementary School, Howard County police spokesman Steven E. Keller said.

Ayres was charged with child abuse, sexual assault and assault and battery and was being held today at the county detention center in Jessup on $10,000 bond, police said. He could not be reached for comment about the charges.

Ayres, a Columbia resident, was arrested at the school after police received a parent's complaint, Keller said. The child, also of Columbia, was not physically harmed in the incident.

Gary J. Arthur, chief of Howard's recreation bureau, said the alleged incident was the first known case of its kind in the history of the county-run day camps, which 1,800 children attend each summer.

"For a public agency serving kids, this is definitely a very sad thing," said Arthur, adding that Ayres' arrest has prompted officials to review the department's hiring practices.

Ayres, who was discharged from the U.S. Air Force several years ago, was recommended for the Howard job by recreation officials in Baltimore County, Arthur said. Ayres worked in Howard for six weeks last spring as a youth lacrosse and softball instructor and was hired as a $200-a-week recreation leader for the six-week summer program, which ends today.

"He was an exceptional employe in the quality of his skills and his ability to teach kids," Arthur said.