IT HAS TO be a disappointment that Fairfax County Executive Robert J. O'Neill is moving on already. He was selected after a nationwide search and with much fanfare only two years ago. Now he has announced that he will resign to head the National Academy of Public Administration. The work he began in Fairfax -- the reform for which the Board of Supervisors hired him -- is far from complete.

Mr. O'Neill certainly moved things in a positive direction. He focused the county government on revitalizing Fairfax's older neighborhoods. For a county that has grown so quickly for so long, the challenge of suburban renewal requires a whole new mind-set. But as Fairfax comes closer to being fully built out, revitalization will become more and more a crucial issue, as for other suburbs in the Washington area.

The county executive also labored to make the 11,000-employee bureaucracy more responsive to taxpayers and to bottom-up initiatives from workers. By most accounts, that project still has a long way to go, but it has been put on track.

Mr. O'Neill survived a couple of well-publicized setbacks. His process for selecting a police chief was challenged, though his nominee was eventually approved. He failed to streamline the parks and recreation department as he hoped. Such bumps in the road aren't all that surprising, and they don't seem to have caused his early departure. He is moving to take advantage of a job opportunity, not out of frustration.

Still, his departure provides a chance for the board to examine how it could reduce such frustrations for the next executive while accelerating the reform process it claims to favor. The supervisors should ask whether they have taken themselves as far out of the micromanagement business as they could. Fairfax is a county of 929,000 people. It likely will work best with 10 supervisors setting policy and one manager implementing it, not with 11 managers. Making that division clear also would be the best way to attract a qualified successor to Mr. O'Neill.