A 17-year-old Anacostia High School student was arrested and charged with assault with a dangerous weapon yesterday after he told one of his teachers that he had accidentally fired at a Metro bus, wounding one early-morning commuter, D.C. police said.

The passenger, Mary Bryant, 32, of 3856 Holley Ter. SE, was treated at Southeast Community Hospital for a gunshot wound in the right hip shortly after the 7:15 a.m. incident. She was released after treatment.

Police said the youth was arrested by an officer assigned to the high school after he told his teacher that while cleaning his father's shotgun on the balcony of his home on Douglas Road SE, the gun went off. The charge hit the bus. A second shot was fired, police said.

According to police and Metro reports, the D5 Mount Rainier bus, occupied by 25 District-bound commuters, was moving through the intersection of Douglas and Stanton roads SE at about 7:15 when, a Metro spokesman said, the driver "heard what sounded like several fircrackers going off."

One-half block later, the spokesman said, Bryant felt a stinging in her hip, looked down and determined that she had been hit.

The driver stopped the bus at Douglas Road and Pomeroy Street, off-loaded the passengers and summoned police, who found two holes in the right side of the bus and removed a slug from a seat for ballistics tests.