IN MUCH THE WAY he has handled all too many important decisions over the last decade, Walter Washington managed to stall until the final moments before officially announcing that he is running for another term as mayor. Having been more than a little critical of his administration, we won't keep you waiting for our reaction to his candidacy. It's time for a new mayor. While it's still early to determine who among the challengers will offer the best prospects for leadership of the city over the next four years, Mr. Washington already has a record in the office - and it is one that has pointed up increasingly the necessity of a change in the top ranks of city hall's executive branch.

To argue for a new mayor, moreover, is not to dismiss the contributions that Mr. Washington has made to a city that he clearly loves. As the presidentially appointed commissioner for nearly seven years, he assisted the community through a trying transitional period as it crawled out from under the heavy colonial thumb of Congress to modified self-government. Indeed, when he ran to be the city's first elected mayor under the charter, the fact that he had "paid his dues" led many a voter to conclude that he deserved the honor that first time out - as well as the chance to show what kinds of positive changes could happen under the new system.

It is this test that Mr. Washington has failed. He was a great commissioner, but a commissioner is not what this city needs anymore. Though Mr. Washington's backers are now talking about presenting a new image for the campaign - and though the mayor has shown a little more energy of late - there's still far too much tired blood in the top echelons of the executive branch. Up to now, Mr. Washington has failed to behave substantially differently as an elected mayor than he did as a White House appointee. And if it takes an election to generate this effort to make a "new mayor" out of Walter Washington, what is supposed to impress people between campaigns?

Instead of moving with enthusiasm to exploit new opportunities, the administration has suffered from Mr. Washington's overdeveloped sense of the impossible, his inability to move efficiently and decisively and his blind loyalty to top aides who have failed to help the very citizens who need help the most.

So we can't think of anything that Walter Washington could say or do at this point that would alter our view that this community needs a change in the mayor's office. How the other talented candidates see the shape of such a change is what should be most interesting in the months ahead.