THE MAD DASH to slice, dice and develop Loudoun County continues apace, with a Board of Supervisors seemingly determined to take irreversible actions with astounding dispatch. Under the guidance of six Republicans who favor heavy growth, every session of the Loudoun supervisors brings another surprise move: reversal of a sound planning policy established by their predecessors; a sudden rezoning with little or no notice; or a reduction of rates charged to developers to help fund new services such as roads, schools and recreation.

The latest unsubtle move came Tuesday when the six members approved a 500-unit housing development on a family farm of their political patron saint, former county board chairman Dale Polen Myers. As reported by The Post's Michael Laris, Ms. Myers, a champion of fast-forward development during her term as chairman, served as the top campaign strategist for two of the supervisors and was a chief engineer of the GOP takeover of the board last year. She has remained deeply involved in county politics since her defeat in 1999 by current board chairman Scott K. York (I), a slow-growth advocate summarily stripped of his leadership powers by the current majority when it took over.

The board voted 6 to 3 to rezone the property, paving the way for single-family homes, townhouses and condominiums -- three times the number of residences that would have been allowed had the board not acted. Supporters of the move said the development violates no housing density policies set by the previous board, but even if that's so, is this the way and pace Loudoun residents want to accept?

Back to those rates that developers should pay: According to figures prepared by the county planning staff -- a professional group now largely ignored or gracelessly countermanded -- the costs of building capital facilities such as schools for a 500-unit development would cost the county from $5 million to $6 million more than it would cost to do so for the 163 units under the previous plan.

What will the supervisors do next -- sell off county land being held for recreational use to developers? Growth is inevitable, but no-holds-barred development is not the way to go. If anxious Loudoun residents don't press their lawmakers in Richmond as well as at home to stick to a reasonable pace, the fastest-growing county in the country will develop into a national model of reckless land use.