I begin hearing the sounds of Fairfax County growing at 7 o'clock in the morning when the bulldozers on the other side of my driveway start pushing around the lumpy tan clay where 185 apartments have just been built. On the way to work, I drive past the Cockrill farm on Hunter Mill Road and notice a sign newly placed in the south cornfield: "Previewing Soon, Sunnyside, Corbitt Homes." Elsewhere in metropolitan Washington, circumstances often have conspired to frustrate growth even when it has been avidly courted. Prince George's County has some of the loveliest landscape found anywhere.It has enough sewer to handle its needs till the year 2000. But the county's image is such that Maryland homebuyers will pay nearly $9,000 more for the same house in Anne Arundel County. Montgomery County has a 24-carat image, but there is no more sewer. Arlington and Alexandria are essentially built out. That leaves Farifax, which has the image, sewer and land. With a fifth of the region's population, it is the site of more than one-third of its building permits. It is boom time in Fairfax. The boom has claimed most of the land best suited for development. What is generally left is land with problems: poor soils, steep slopes, high water table, airport noise, proximity to environmentally sensitive areas (like the Occoquan Reservoir). Last year, the county board of supervisors, following the suggestion of their own master plan, decided to deal directly with this problem and proposed setting aside large sections of the county - near the reservoir and in Great Falls along the Potomac River - for the lightest development (5- and 10-acre tracts that real-estate people call "estates"). But when some landowners howled, supervisors did everything but hide under their desks. The downzoning proposal was hastily withdrawn before it could be examined at public hearings and possibly be redrawn more equitably. The supervisors wearily explain that the Virginia courts have left them little space in which to maneuver on land-use issues - though most of them will agree that Fairfax's rapid growth is a threat to the county. Richard J. O'Brien is a member of the Planning Commission, which looks at land-use issues and makes recommendations to the supervisors. He is upset by what he sees as the failure of the county government to raise its vision above the dust of the bulldozers and give some attention to larger issues - like protecting the land near the Occoquan Reservoir or sorting out the transportation mess. He and his colleagues recently finished their annual review of the county's master plan. He says the commission got bogged down in a monstrous agenda of more than 200 items. There was no format, not to mention time, to ask whether Fairfax actually has a planning process that can serve what the supervisors, in 1973, said was their first priority: "to improve the quality of life through local and regional comprehensive planning and development control . . ." The supervisors have taken a step - a baby step, some impatient observers might say - to protect the Occoquan. They will now require developers to take some additional steps in controlling pollution from storm-water runoff. Even so, some officials acknowledge it's possible that, if growth continues, the Fairfax County Water Authority will have to filter reservoir water with elaborate carbon columns: the system would cost $28 million to build. Might it be better to spend part of that sum to buy higher-density development rights to all of the critically located land in the Occoquan area? If $82 million could be spent on another project to stop sewage from polluting the reservoir, why couldn't, say, $10 million be spent on this one to stop pollution from urban runoff? It has been five years since the supervisors came out of the boiler room and asked - out loud - where their policies on land use were taking the county. They do not need another forum where neighborhood groups can press forward their parochial, albeit legitimate, grievances. What they need is something like the all-day Chautauqua on growth held recently by the Montgomery County Planning Board. Under a green and white striped tent in Wheaton Regional Park, citizens, officials, developers and experts of all sorts and persuasions had a free-for-all. Though the debate was spirited, it was not contentious. The mid-day break for chicken, potato salad and music kept the atmosphere polite and even at times congenial. Imagine that at the typical public hearing. But Fairfax County had better hurry, before there's no longer a place to pitch a tent and not be drowned out by traffic going to and from the newest subdivision.