The body of a 19-year-old woman was found early yesterday behind the Walker Mill Junior High School in District Heights, according to Prince George's County police.

Police and school officials said that the body of Patty Alston of 915 Brooke Rd. in Capitol Heights was found by a boy on his way to school in a playing field a few yards from the building. They have no suspects.

Lt. Robert Miller, head of the homicide unit, said that there were tire tracks from a motor vehicle on the ground by the body. Miller said last night that the cause of death had not been determined by state medical examiners, but that detectives believe Alston may have been struck by a car. Her family reported her missing yesterday morning.

There are parking lots on three sides of the school, but no road behind the school were Alston was found. Police could not explain why Alston or a car would be behind the school.

Neighbors said that Patty Alston, a quiet Suitland High School student, lived at home with her mother and younger brother.

Alston is the second young woman in her neighborhood to be killed or to die mysteriously in the last two years. In April 1981, police identified a body in an Anne Arundel County park as that of Dawn V. Anderson, 18, who had been missing from the same section of Capitol Heights since the previous month. Anderson was a popular cheerleader who had graduated from Bladensburg High School.