The Fairfax County School Board last night approved a compromise plan to delay construction of the controversial Braddock Park Intermediate School for two years, until a scheduled opening in the fall of 1986.

The board's decision came despite personal appearances by John F. Herrity, chairman of the Fairfax County Board of Supervisors, and Springfield Supervisor Marie Travesky urging the board to stick to the original fall 1984 opening date for the planned new school, which was authorized in a 1982 bond referendum. The school would be located at the corner of Braddock and Union Mill roads in West Springfield.

The five-year school construction plan the board approved last night had called for postponing the Braddock Park opening until 1988.

School officials had urged postponement because changing enrollment figures suggest the Braddock Park school might not be used to capacity in its first years.

School board member Toni Carney, who represents the Springfield district, told the board, "It will not be a sin, the world will not stop spinning on its axis if for once in 13 years there is an empty classroom in the Pohick watershed area . . . . We don't build facilities to open at capacity."

In other actions, the sanctioning of Mount Vernon High School by the Virginia State High School League took a surprising turn when representatives of several local athletic associations spoke in support of the VSHSL's decision. At its Dec. 16 meeting, the Fairfax School Board had approved a resolution criticizing the VSHSL and asking the General Assembly to investigate the group's activities.