The Fairfax County School Board voted last night to approve a five-year $196 million classroom construction plan and to urge replacing 362 aging school buses within two years.

The board unanimously approved the construction plan after agreeing to Chairman Mary E. Collier's motion to add the renovations of two high schools, costing $15 million, to the two already included in the staff-recommended proposal.

The plan provides for constructing seven elementary schools, an intermediate school, 11 elementary school additions and three special education centers in fiscal 1987 through 1991.

Also approved were extensive renovations to 10 elementary schools, two intermediate schools and gymnasium and music rooms at 11 other elementary schools.

The construction must be approved by the county Board of Supervisors, and voters must pass a bond referendum to provide the necessary funds.

The construction is needed because of a baby boom and the addition of special programs requiring more classrooms, board members said.

Collier, who had questioned why new schools were proposed near schools that recently were closed, said she was persuaded that many of the new buildings are needed to meet board-mandated reductions in the size of classes.

In agreeing to ask the Board of Supervisors to replace the older buses within two years, the School Board yielded to parents' complaints that the proposal before the board for a three-year replacement plan would be too slow.

Two children and the bus driver suffered serious injuries in the crash of a Cooper Intermediate bus last Oct. 22, which also injured 11 other children.

The bus, built in 1973 and carrying 27 students collided with a maintenance truck on Georgetown Pike in Great Falls on Oct. 22, then slid down a 20-foot embankment.

Mark Savit, whose child was on the bus, called the three-year proposal "grossly inadequate" and said it would mean that 14- and 15-year-old buses still would be on the road next year.

School officials repeatedly have said that buses built before 1978 are not unsafe.