Allan Dale Johnson, 41, a Prince George's County police corporal from Forestville, died early yesterday of injuries he received Monday when he was struck by a car while writing a traffic ticket on the Capital Beltway.

With him when he died at Prince George's General Hospital were his wife Sylvia, his daughter Cynthia, 22, his son Grant, 7, and several county police officers.

Johnson, originally from Pennsylvania, was a 19-year veteran of the police force and would have been eligible for retirement next August. He was in charge of the six-man motorcycle unit, a part of the police Special Operations Division.

Shortly after 6 a.m. Monday, Johnson had stopped a van beside the beltway's northbound lanes in Capital Heights and was standing behind it writing a ticket when a car ran off the roadway, hitting him and the back of the van.

Johnson was flown by helicopter to Prince George's General Hospital, where he died yesterday.

The driver of the car, Alan Y. Zagorny, 26, of Forestville, suffered a broken jaw and nose in the crash and was admitted to the hospital. County police are still investigating the accident. No charges have been filed.

Yesterday, officers of the special operations division helped each other place symbolic black bands over their badges. Capt. Robert Phillips, commander of the division, said officers were taking turns staying with Johnson's family.

Johnson's commanding officer, Lt. David Mitchell, described Johnson, who was called "A. D.," as an exceptionally professional officer with a military air.

Before becoming the first officer in the new motorcycle unit in 1974, Johnson had worked as an undercover robbery detective.

Phillips said Johnson would jog 10 to 15 miles a day through the Forestville area and was preparing, along with some other motorcycle officers, to run in his first marathon.