A 48-year-old resident of Forest Haven, the District of Columbia's institution for the mentally retarded in Laurel, was beaten unconscious last night in the cottage he shared with about 40 other residents.

The victim, a resident at the facility for 40 years, was taken to Prince George's General Hospital where he was in fair condition early today undergoing treatment for head injuries.

Before being taken to the hospital by the Laurel rescue squad, and man regained consciousness briefly and said he had been beaten by other residents, according to Albert Russo, director of the D.C. Department of Human Resources, which operates the facility.

Russo said six staff members were on duty when the attack occured in a section of Curly Cottage, the division housing profoundly retarded residents, but none was aware of the incident.

Russo said a staff report indicated that the man was found at 8 p.m. "badly beaten and unconscious." As of late last night, neither Russo nor Forest Haven personnel could say precisely how the incident had occurred.

In recent years Forest Haven has fought a losing battle to upgrade the crumbling physical facility. The institution also has suffered severe criticism over staff shortages, violence among patients and alleged abuse of patients by staff members.

In 1976 parents of Forest Haven residents sued the District, alleging staff negligence and abuse of patients. The federal government supported the parents in the suit. After two years of litigation, the city agreed to close down Forest Haven after moving all patients back into the community. t