The Fairfax County School Board approved a $519.9 million construction plan last night that would build five new schools and renovate dozens of others by 1993.

The 10-to-0 vote came after the board added six elementary schools and one intermediate school to the list of renovations proposed by Superintendent Robert R. Spillane.

The additions bring to 24 the number of elementary schools scheduled for extensive renovation, and four the number of intermediate schools. Three high schools also would undergo extensive renovations.

The spending for new schools and renovations must be approved both by the Board of County Supervisors and voters in bond referendums. Spillane is to recommend to the School Board April 14 what portions of the building plan should go to a vote in November, with an estimated price tag of $150 million or more.

Repairs to aging schools built 20 and 25 years ago were among the hottest issues in the construction plan. The County Council of PTAs had urged extensive renovations to 24 elementary schools, six intermediate schools and six high schools.

Board member Kohann Whitney, one of those who urged adding more schools to the renovation list, said the repair needs are so urgent that if voters turn down bond issues for the work "then we can go from band-aids to tourniquets."

Proposed construction for fiscal 1989 to 1993 includes four elementary schools and one intermediate school and additions at eight elementary schools, most of which the board has tentatively approved but not financed. New in this year's approved plan is money to plan two more elementary schools, one additional intermediate school and one additional high school, all to be built in the county's southwestern growth area after 1993. Also included is purchase of land for three additional elementary schools.

Renovations also include air conditioning for the 87 schools and special education centers that are not fully air conditioned, as well as millions of dollars for new carpets, roofs, boilers and asphalt.

Although the last school bond referendum, a $146.1 million proposal in 1986, was approved by a wide margin, some school officials are concerned that growing competition for taxpayer dollars with road-building needs could be a problem.