The 16-year-old son of a widowed Southeast Washington woman was shot and killed on an Anacostia street yesterday by robbers who tried to take the big portable radio friends said he carried everywhere he went.

Donnell Plater, of 1448 Congress Place, described by a neighbor as a "wonderful boy," was shot in the chest about 5:40 p.m. near the intersection of Martin Luther King Avenue and Lebaum Street, SE, just south of the St. Elizabeths Hospital grounds.

Police arrsted three youths a short while later after stopping a car in the 4400 block of South Capitol Street. Detectives said the three were charged with homicide.

According to authorities, the youth was carrying both the briefcase-size radio and a bag containing clothing he had just bought when he and a companion were approached by several youths, one of whom demanded the bag and the radio.

Investigators said that at that point a shot was fired, striking Plater in the chest. He was pronounced dead two hours later at D.C. General Hospital. It was not immediately known why the assailant fired, detectives said.

Friends and neighbors said that the victim, a junior at Ballou High School, held a part-time job and was scheduled to be paid yesterday. They speculated that he had used his salary to buy the clothing he was carrying when the assailants approached.

Plager, whose father died about four years ago, had three older sisters, all of whom live in the Washington area.

Neighbors said he was fond of basketball, boxing, and the rock music that constantly flowed from his portable radio.