An unidentified Hyattsville man was shot last night by two D.C. policemen and then run down by a passing motorist at 17th Street and Benning Road NE after the man threatened the officers with a knife, police officials reported.

The 23-year-old victim was struck in the arm and shoulder by police bullets, and it was unclear early today whether he died as a result of these wounds or from being struck by the car, police said. An autopsy is scheduled today.

Officials said the incident began about 10:30 p.m. when officers James Washington and Darryl Evans stopped an auto in the 1800 block of Benning Road after it had made an illegal left turn.

The driver agreed to sit in the back of the officers' patrol car while his permit and registration were being checked, officials said, but a struggle broke out between him and Washington, and the man bolted from the cruiser.

As the officers got out of the car, the man pulled a folding knife with a five-inch blade and threatened them, officials said. They said both officers fired their revolvers when the man refused to drop the weapon.

Then, with the officers in pursuit, the man ran east on Benning for about a block. There, officials said, a motorist whom police later identified as a private detective shouted from his car to the fleeing man that he was a law enforcement officer and ordered him to halt.

When the man continued to run, the detective drove his car into him, police said. The man was pronounced dead at D.C. General Hospital about 45 minutes later.

Both officers have been placed on routine administrative leave pending the outcome of a grand jury investigation, officials said.