Patrick Dutch, the severely retarded man who died July 9 after being left unnoticed for five hours in the back of a van, died of heatstroke, and his death was ruled an accident, Jonathan L. Arden, the District's chief medical examiner, said yesterday.

Dutch, 41, was found in the rear seat of a van that was supposed to take him from his group home on Quincy Place NW to a day program in Southeast. A driver and escort from the group home, operated by D.C. Health Care Inc., dropped off seven other residents before returning to the home. Five hours later, they noticed he was missing, and as staff members from the home were searching for Dutch in the area around the day program, he was discovered curled up in the van's back seat.

Arden said heatstroke was difficult to diagnose in Dutch's case because the most visible symptoms--an elevated body temperature and lack of sweating--are generally observed before a victim has died.

The judgment in Dutch's case was made because "he was physically well at the time that he was in the van, was found dead hours later, and had been subjected to extreme environmental temperatures by virtue of being inside a closed vehicle on an extremely hot day," Arden said. The high temperature recorded in the District on July 9 was 99 degrees.

Dutch, who could not hear or speak, lived in the District's Forest Haven asylum for the retarded in Laurel from age 4 until the city shut it down in 1990, according to city officials and care providers. He then entered a D.C. Health Care group home on Georgia Avenue NW and was transferred to the Quincy Place home in 1993.

Mayor Anthony A. Williams has ordered the city's health, human services and police departments to investigate Dutch's death. Adrienne Buckner, acting administrator of the Mental Retardation and Developmental Disabilities Administration, a branch of the D.C. Human Services Department, said last month that routine inspections made by the office since 1993 had not uncovered problems at the homes operated by D.C. Health Care.

A supervisor at the Medical Assistance Administration, a branch of the D.C. Health Department that monitors Medicaid-funded homes for retarded, also described the company as one of the city's better care providers yesterday.

Mary Dutch, the victim's mother, declined to discuss the case.

"With all honesty, the whole agency regrets this incident and we are very sorry he died," said Gracy Stephen, the co-owner of D.C. Health Care, who also said that Dutch's death was a tragic accident. Stephen said Dutch's death has prompted the company to institute tighter procedures to make sure that all residents are correctly dropped off and picked up.