An 11-year-old boy was killed yesterday when the elevator in his northeast Washington apartment building began moving apparently as he tried to climb out of it between floors, D.C. police reported.

Police investigators said it appeared that the victim, Anthony Bass, of 2504 10th St. NE, had been riding the elevator with his 3-year-old cousin, who was not injured, about 5:30 p.m. when the car stopped between the lobby level and the basement of the five-story building.

Anthony apparently then pulled open the elevator's safety gates and a heavy metal door and began clambering down to the basement level when the car began moving upward, crushing his head between the car and the elevator shaft, police and building residents speculated.

A woman tenant in the lobby opened the manually operated elevator door to board moments later, and her screams alerted other building residents, who summoned police and an ambulance. The boy was pronounced dead on the scene.

The victim's mother, Sabrina Hale, arrived home from work minutes after the accident and was taken by friends to the Washington Hospital Center where she was treated for shock.

Told of the incident by neighbors, the boy's distraught father, Bernard Mooten, 30, began pounding his fists against a hallway wall, crying "Oh no. Oh, no." Mooten said Anthony, a 5th grader at Harriet Tubman Elementary School, studied every day, kept his school books in order and "was a good kid."

The D.C. Industrial Safety board is investigating the incident, as is the D.C. police department's homicide unit, officials said.