THE JOB of school superintendent has become so difficult that it is more and more common for those who hold it to choose early retirement. Such was recently the case in Montgomery County. Equally common are situations in which superintendents are fired or demoted because they haven't met the demands of the job. Such was the case recently in the District of Columbia. Others can no longer stomach the constant second-guessing of overzealous school boards. And some anticipate the "terrible toos" -- too many people expecting too much too soon -- and decide to quit before the ax falls.

The fact that none of these factors -- not one -- was present in Prince George's County is what makes the loss of Superintendent John A. Murphy so puzzling, unfortunate and damaging. Mr. Murphy was not burned out but had been rather eager to get on with the next phase of transforming the county's schools into a top-flight system. He had not failed to meet the demands of his job, but had in fact exceeded some goals. Generally, the school board and many parents greatly admired his work. But Mr. Murphy is nevertheless headed for the top education post in Charlotte, N.C., the board has accepted his resignation, and the how and why of that deserve a final airing.

By now the story is pretty clear: how Prince George's officials overreacted to the possible loss of Mr. Murphy last year by offering him a decade-long contract and a monumental raise and how black leaders were outraged over a lack of consultation and by the idea that an increasingly black school district might enter the next century without the option of a black superintendent. Mr. Murphy rejected the offer, and it was retracted. Lost in the shuffle was the fact that John Murphy had done much to elevate the Prince George's schools in image and in substance, for black students and whites. Lost, too, was the fact that the school board, for all practical purposes, let him go without much of a fight.

The lessons here are many and varied. First, for the benefit of students, this situation could have been resolved by the board, perhaps with the same result, some time ago. The county now finds itself in a spot in which it will have to scramble to have a new superintendent in place for the start of the September term. The superintendent-searches of most of the other large school districts around the nation are either over or reaching completion. And there is another issue here -- the issue of whether a school board has the collective vigor and imagination to back and reassure a superintendent who is under fire for reasons that appear to have nothing to do with his performance. The next person to worry about this last point could well be the next person the county tries to hire.