The Loudoun County School Board voted unanimously last week to present a five-year, $4.5-million program to the Board of Supervisors next month to build three elementary schools, one middle school and one high school by 1990 in the fast-growing eastern end of the county and the Leesburg area.

No land costs will be included in the request, the board said, because all necessary land will be made available to the county by developers in exchange for considerations on their projects.

The enrollment projections on which the building program is based were derived from building permits approved by the county and from construction anticipated over the next 10 years. The board will also ask the supervisors for permission to choose an architect by January to design the schools.

School Superintendent Robert Butt said the board took the unusual action of preparing for construction before selecting sites because it hopes to have the first two elementary schools -- one in Leesburg and one in eastern Loudoun -- open by the fall of 1988.

In a report to the School Board, Assistant Superintendent George Atwell said the supervisors should be asked to provide funding by January 1987. According to Butt, schools have been successfully funded in Loudoun County through bond referendums with the county's AA rating from two prestigious rating houses in New York. "The climate is right" to ask for such a referendum, he said.

Total capacity for the five new schools would be nearly 5,000 students, the report said. According to county figures, projected growth in eastern Loudoun through 1990 is 1,059 housing units per year. Projected elementary school enrollments for the area have nearly doubled since 1984, from 774 to 1,414, the report said.

Butt said the school officials discussed projections with the supervisors about a year ago. "I didn't let the parents and kids in; the supervisors approve development," he said. "Loudoun people want good schools. And we want the seats ready when the kids get here."

Board of Supervisors Chairman Frank Raflo said the supervisors are aware that five new schools are needed, but declined to comment on the report until the board has had a chance to study it.

In other business, the board heard a recommendation by compensation committee chairman Leonard Warner to increase teachers' salaries by 11 percent next year, which would add $4 million to the 1986-87 school budget.

This would bring the salary of a teacher with a bachelor's degree and no experience to $20,000 from the current $17,500 and would make starting teachers' salaries in Loudoun the highest in the Washington metropolitan area.

Warner also recommended a 20 percent raise for secretaries and clerks, 15 percent for school aides, 9 percent for other classified personnel and 7 percent for administrators and supervisory personnel.