THE PRINCE George's County Board of Education should try once more to persuade School Superintendent John Murphy to remain on the job. The timing here is crucial for several reasons. Mr. Murphy is now one of five semifinalists for the superintendent post in Boston, and a decision there is expected by January. Moreover, the Boston situation shows that some school systems are already far ahead in their leadership searches, which leaves Prince George's poorly positioned in terms of timing its own negotiations.

Salary may not be the primary issue here. Mr. Murphy has announced his intention to leave Prince George's even though the school board there recently made him the region's highest paid superintendent, with a new salary of $120,000 and a yearly annuity of $15,000. Mr. Murphy has repeatedly said he wants to finish his career in Prince George's and has sought such assurances from county officials. Roughly 18 months remain in Mr. Murphy's current contract.

Now the board should vote on whether it will pledge to renew Mr. Murphy's contract when it expires; if so, the offer must be made soon. If that effort fails, the board must rapidly move forward in seeking a replacement.

The D.C. public school system is also in the market for a new superintendent, and it should pay close attention to Prince George's. If Prince George's is unable to keep Mr. Murphy, the D.C. Board of Education superintendent search committee would do well to inquire about his interest in moving to the District.

Under Mr. Murphy's leadership, the Prince George's schools have: 1) increased black student involvement in advanced placement courses and raised college attendance among blacks by 25 percent; 2) raised achievement levels and test scores of even the poorest students, while ensuring that other students also improved to a level commensurate with the best school systems in the region; 3) created a marvelous system of magnet schools; 4) gained the confidence of local businesses and raised millions of dollars in private money and grants.

Just as it would be outrageous to suggest that minority applicants should not be considered for top posts in predominantly white school systems, it would be ludicrous to overlook Mr. Murphy for the D.C. schools because he is white. Prince George's probable loss need not be the region's loss as well.