The man walked into the Prince George's County liquor store, showed what appeared to be marijuana, looked at the off-duty policeman working behind the counter and demanded: What are you going to do about it?"

The officer came out from behind the counter. The man fled. The officer was found near the store, a few minutes later, shot in the head, possibly with his own gun, apparently after a struggle.

He died late last night at Prince George's County General Hospital.

An intensive manhunt, involving police on foot, in cars and in a helicopter was under way last night, around the area of the shooting, the intersection of George Palmer Highway and Columbia Park Road in Landover.

The officer was identified as Antonio M. Kelsey, 22 a graduate of the District's Coolidge High School and county policeman since December, 1978. dThe incident that led to his death began about 9 p.m. at Cox's Liquors, 7200 George Palmer Hwy.

A cashier at the store said that the officer, who worked intermittently at the store in his off-duty hours as a security guard was seated behind the counter on a stool when a couple entered and the man displayed what seemed to be marijuana.

The cashier said that it was well known that off-duty police officers worked at the sotre and that she suspected the man knew he was showing the material to a policeman.

The cashier said she believed the man was intentionally taunting the officer, demaning, "What are you going to do about it?"

As the man's companion began pushing him out of the store, the officer sprang from his stool, came out from behind the counter, and began to pursue the man.

The officer was found on Columbia Park Road, around the corner from the store and a short distance away.

Authorities said the revolver he wore out of slight in a holster was missing. The theorized that it may have been taken from him during a struggle, and that he may have been shot with it.

A Maryland state police helicopter took the officer to the hospital where he later died.

No arrest have been reported as of earyl today.