"OUTSTANDING PERFORMANCE . . . You have performed in an exemplary manner . . . great strides forward . . . Your accomplishments have exceeded [our] expectations . . . We have come a long way in the past several months, and it is clear that a sizeable share of the credit belongs to you and your excellent staff."

Would you believe that those are excerpts from a recent letter addressed by the District Of Columbia School Board to the District of Columbia's Superintendent of Schools? It is not an easy thing to believe, if one is at all familiar with the dismal history of that particular relationship over the past 10 years or so. But it is true; the board said these nice things, and more, in a recent whose significance in historial terms can be fully appreciated only after you've cast your mind back to the dark before Mr. Reed took over his present job.

Surely you will not have forgotten the Barbara Sizemore era. Such was the intensity of her continuing controversy withe the board that her successor, it could be said, had no place to go but up. But the Sizemore debacle was not an isolated case. Open warfare between the board and one or another superintendent had been the normal state of affairs for years. The broad outlines of the controversy in each case were fairly similar: The school board hired an educator from outside the school system with much fanfare and talk of innovative educational methods, and shortly thereafter the relationship degenerated into an exchange of accusations that the superintendent was incompetent, that the school board was interfering - and on and on. This decade of continuous controversy sapped the morale of teachers and parents, and relegated the school's forgotten constituents - the students - to the status of political pawns.

So the impressive evidence now before us of a harmonious and constructive relationship between the school board and the superintendent signifies much more than a welcome change from the Sizemore days. It signifies a state of affairs in the District school system the likes of which we haven't seen in this cirty fror a good many years. We would not wish ot overdo it; many extremely difficult problems remain to be solved. What's important, however, is that while these problems r may persist for some time, relations between the board and the superintendent are such that both can at least concentrate their time and energies on problem-solving, as distinct from guerrilla war.

Mr. Reed, a 22-year veteran of the school system, has brought to the top job a host of assets. His considerable personal charm and frankness have won friends for the school system. His leadership immediately improved moral within the school bureaucracy. His managerial know-how served him well in his efforts to straighten out the administrative chaos that had plagued the schools for years. The board's letter mentions one of the most bothersome of these difficulties: errors in paychecks. Since Mr. Reed took office, the letter states, payroll errors are "the rare exception rather than the rule." Other administrative matters, the letter adds, are also done well routinely.

Mr. Reed and the board still must address tremendously difficult problems, the most important of which have to do with improving the quality of instruction and the quality of student performance. This is an assignment they're aware of; this fall Mr. Reed's staff will install in the schools a comprehensive plan for improving teacher and student performance that has been two years in preparation. Given the magnitude of the task, no one should expect quick success. But the chances of progress being made are immeasurably brighter as a consequence of the constructive and harmonious relationship that has developed, after a decade of turmoil, between the superintendent and the board.