Maurice Johnson, 18, the Suitland High School senior arrested Monday in the shooting of another student, was free on bond at the time on an armed robbery conviction for which he was sentenced yesterday to 15 years in prison.

Johnson, accused of wounding Bruce Everett Void, 18, with a sawed-off shotgun in an incident on the school grounds Monday, could have been suspended if his robbery conviction had been known to school authorities.

Peter Blauvelt, head of security for the school system, said yesterday the schools were unaware of Johnson's conviction in the robbery of a man at gunpoint in the parking lot of a Suitland restaurant last March. Johnson had pleaded guilty in August to armed robbery and firearms charges in that holdup and was released on bond pending sentencing.

School security officials noted that Johnson had previously attended a high school in the District of Columbia and entered Suitland High this fall. "There is no way we would have knowledge that this young man pled guilty and was out on bond," said Blauvelt. "The school system is not playing with a full deck."

Prince George's school policy gives the school superintendent power to suspend a student who has been charged with a serious crime if the superintendent believes the student's presence could be dangerous to other students.

Yesterday, Prince George's Circuit Court Judge Samuel W. H. Meloy sentenced Johnson to concurrent terms of 15 years for the armed robbery and 10 years for using a handgun in the robbery.