Benjamin Wilson Jr., considered to be one of the finest high school basketball prospects in the country, died today after being shot Tuesday in a sidewalk altercation with some teen-agers near his school. He never regained consciousness.

Wilson, a 17-year-old senior at Neal F. Simeon Vocational High School on the city's Southwest side, was a power forward on a team that won the 1984 Illinois state championship last March, and seemed headed for glory again this season.

The 6-foot-8 senior, who was described by Principal Ned L. McCray as "a good student, not a dumb athlete," was a B student and an all-around player already heavily recruited by a number of major colleges. Wilson's death plunged the 1,800-student school into gloom, and hundreds wept, moaned, and shouted with grief during a morning-long memorial service in the gym today. His teammates were not allowed to attend because their coach feared they might become too upset.

The shooting occurred Tuesday afternoon, as Wilson was accompanying his girlfriend and another girl on a walk in the neighborhood during lunch hour. Although not married to her, Wilson had fathered a 2-month old son by the girl, according to his school friends. School officials refused to comment on his relationship with the young woman.

The Simeon students were confronted on a sidewalk by a trio of teen-age boys from another school. According to police, who gathered numerous eyewitness accounts, Wilson reportedly "bumped into" the trio, then apologized.

Instead of accepting his apology, one of the trio pulled a pistol and shot him twice. One bullet struck and destroyed his liver, and the other severed a major abdominal artery. The three fled as Wilson slumped against a fence.

He was taken by ambulance to St. Bernard Hospital nearby, and doctors worked for more than five hours to save his life. As the surgery proceeded, friends and students crowded hospital corridors, holding an impromptu prayer vigil. Others gathered outside and waited through the cold night.

Because of massive bleeding, Wilson required two complete full-body transfusions. But hospital officials said the victim had arrived with no pulse and their efforts to save him failed. He was pronounced dead at 6 a.m. today.

The shooting captured headlines here and across the country. An aroused and saddened City Council demanded a crackdown against teen-age gangs, which plague many Chicago neighborhoods, including the middle-class residential area around Simeon. McCray, the Simeon principal, described his school as "an oasis, an island in a sea of troubled waters. People can be accosted leaving the oasis, as Ben was."

Two youths, one 15, and one 16, were arrested and held without bond in the killing. They were identified as William Moore and Omar Dixon, students at Calumet High School and cousins. They were charged with murder and attempted armed robbery and will be tried as adults. Police have recovered a 22-caliber pistol that they identify as the weapon used in the slaying.

The third youth who was present has not been charged and is said by police to have turned state's evidence and already has testified before a Cook County grand jury.

Under state law, the two suspects cannot get the death penalty because of their age. A grandparent of each suspect contacted today said both were innocent.

Wilson, who shaved his head as a trademark, was rated the nation's No. 1 high school basketball player last summer after showcasing his talents at a summer camp at the Athletes For Better Education Camp at Princeton, N.J. His emergence on the national high school scene propeled Simeon to a top ranking in several national preseason polls. Wilson had the versatility to play guard or center as well as forward. He averaged 20 points a game and shot 75 percent last year.

"I thought he was the best player in the country," said De Paul Coach Joey Meyer, who had been intensively recruiting Wilson.

The Simeon team tonight was headed for Rockford, Ill., 90 miles west of Chicago, for a tournament. Simeon's opponent tonight was Evanston Township High School in a rematch of last year's Class AA state tournament final. In that game, Simeon beat Evanston, 53-47. Tonight, Simeon won, 71-52.