A 60-year-old counselor at a school for emotionally disturbed children in Prince George's County has been charged with child abuse for allegedly having a sexual encounter with an adolescent boy, Maryland State Police reported yesterday.

Police said Allen Keys Richards, of 7905 Eagle Ave., Alexandria, was arrested by Virginia State Police Monday night and extradited to Maryland.. Richards was a counselor at Edgemeade of Maryland, a state-supported school in Croom, but resigned May 2, a school spokesman said.

State police had been called in May 1 to investigate a report by another employe who said he had observed Richards in a sexual act with an adolescent patient, police said.

Richards was jailed in the county detention center on $7,000 bond.

Earlier this week, a teacher in a Silver Spring day care center, who had been arrested last month in Montgomery County on charges of distributing pornographic photographs of children, was arrested in Prince George's County while free on bond and charged additionally with 15 counts of child abuse.

Police said Robert A. McCormick, 42, of White Oak, who was also a substitute teacher in Prince George's, has been charged with taking pornographic pictures of children and performing sexual acts with at least a dozen children. McCormick is being held on $60,000 bond.