The Fairfax County School Board voted unanimously last night to hire a consultant to study the possibility of implementing a merit pay system for teachers and administrators.

Although the step was approved after less than five minutes of discussion, the issue of merit pay--linked by many to the question of how to achieve educational excellence already being debated by school officials and teachers nationwide--seems sure to generate controversy in Fairfax.

Robert S. Starr, acting president of the Fairfax Education Association, said after last night's board meeting, "I would have to wait for a proposal before I can comment on any plan." He added that Fairfax teachers are generally opposed to merit pay.

"Who is going to decide which teachers are the best? It's going to pit teacher against teacher. Before you even talk about merit pay, we need to bring the salaries of teachers up to the point where they are adequately paid for what they do," Starr said.

Board member James W. Kitchin of Mason District said after the meeting he felt it "appropriate to get a consultant to take an objective view. This issue is fraught with emotion and passion. Merit pay is not a panacea but it may be worth looking into."

Board member Carmin C. Caputo of Centreville District said, "We hope to get a pilot program implemented by the 1984-85 school year."

The consultant, to be chosen from competing bidders by Oct. 15, will work with a task force of teachers, school officials and civic leaders to review current teacher evaluation programs, incentives and benefits.

The consultant also will make periodic reports on the task force's progress and will submit a final recommendation to the board in April.