The Fairfax County School Board voted last night to give Superintendent Robert R. Spillane a $10,000 raise, bringing his salary to $100,000 a year and making him the highest paid public school educator in the Washington area.

Spillane, who also receives a $10,000 cash annuity, will complete his second year as superintendent July 1, when the raise takes effect.

During his tenure, the school system has moved toward adoption of the area's first merit pay program for teachers, which will include 12.1 percent raises for faculty members in the 1987-88 school year. Spillane's raise is slightly less than that -- just over 11 percent -- but nonetheless was considered a hefty reflection of School Board confidence in him.

Fairfax, with 128,000 students, is the largest school system in the D.C. area.

The board also voted to hire Edward W. Carr as its new assistant superintendent for personnel, at an annual salary of $65,000. Carr most recently worked as a research assistant at the College of William and Mary, and before that was assistant executive secretary of the Virginia School Boards Association.

Board members also voted to accept about $88,000 offered by the county Board of Supervisors to broadcast the biweekly School Board meetings on cable television.

The board also adopted its education priorities for the next school year, for the first time including the development of a long-range plan "to address staffing ratios, class sizes, teaching loads, and length of the school day and year."

All of those changes would be expensive and any reduction in class size would require construction of many new classrooms. School officials say it would be difficult to make dramatic changes in class sizes soon, but they are concerned that some students are leaving public schools for private schools with smaller classes.

The issue of a longer school day and year is mentioned in several of the recent national reports urging improvement in education. Fairfax officials say adding an extra period to the school day would enable students to take more elective courses at a time of increasing academic demands.