IT MUST have been pretty hectic around city hall recently, what with Mayor Washington and his close associates all poring over their various reports on each other for clues to the extent of fallout to come from the Perils of Joseph P. Yeldell and Other Stories. But this executive-branch preoccupation with one department's problems doesn't strike us as a reasonable excuse for a rather disturbing lapse of good judgment on the part of the head of another department. COmer S. Coppie, the city's budget director, somehow forgot to inform the mayor about an important bit of news he picked up from the White House. On Nov. 16, Mr. Coppie learned from a Ford administration official that Mr. Ford was going to cut $10 million from the requested federal payment to the city for the next fiscal year.

It seems that Mr. Coppie kept this piece of intelligence all to himself for two months. As a result, it came as a great big - and disagreeable - surprise to Mayor Washington, the city council and any other local taxpayer who cares about the precarious state of this city's finances when - on Jan. 17 - the White House released the news. In fact, it was the first time that the White House hadn't requested Congress to appropriate the full federal payment authorized in the city charter. Though Congress always trims the requested amount, anyway, Mr. Coppie's communications failure fouled up the city council's budget work, since the approved spending proposals were based on the higher revenue figure.

When Mr. Coppie finally did disclose his secret to the city council at a hearing last week, a few of the members were understandably angry. Julius Hobson said it was shameful, Willie Hardy was stunned, and Marion Barry termed Mr. Coppie's failure to tell the mayor "a beach of trust and sensibility." As for Mr. Coppie, he acknowledge "an error in judgment on my part, a serious error," and said he now believes tat he "could have and should have" informed others. Council Chairman Sterling Tucker was probably closer to the mark with his comment that the development "may be symptomatic of a broader problem. It may suggest too much independence by department heads." Call it independence - or an abdication of leadership by Mayor Washington - but there has been the usual non-reaction from his Honor's office. Another mayor might well have fired, publicly reprimanded or reassigned an aide for making such an error. But mayor Washington, home with a sinus condition, let it be known the other day that Mr. COppie would not even receive an administrative reprimand for his negligence. So now we'll all just have to wait and see how the city's budget requests fare under the circumstances.

President Carter could do everyone here a great service, however, if he would revise Mr. Ford's federal payment proposal and recommend the full authorized payment. The city's elected leaders are asking Mr. Carter to recommend the additional $10 million, and the request is reasonable. If Mr. Coppie is once again the first to get the word of how the new White House feels about it, we do hope that this time he'll share his secret with his boss and, for that matter, with the city council and the rest of us.