A plainclothes D.C. police officer shot and critically wounded a man in Northeast Washington yesterday after the man had confronted two persons with a gun and then pointed the gun at the officer while being chased, police said.

Allen Thacker, 33, whose address is unknown, was reported in critical condition at the Washington Hospital Center with a gunshot wound in the chest.

Police said the shooting took place about 4:20 p.m., when officer Stephen West Sr. and his partner saw Thacker allegedly point a gun at two other men in the 1100 block of Fifth Street NE.

Police spokeswoman Shannon Cockett said that as West aproached the men, they moved into an alley on the east side of Fifth Street NE.

West and his partner followed the men into the alley, Cockett said, where they allegedly saw Thacker slap one of the other men. West then identified himself as a police officer and ordered Thacker to stop, she said.

Thacker allegedly ran down the alley and West followed, again ordering Thacker to stop, Cockett said.

She said that at the rear of 1117 Fifth St. NE, Thacker allegedly turned and pointed his weapon at West, and the officer fired his service revolver once, striking Thacker in the chest.