Prince William is about to start fine-tuning the slow-growth plan it passed 13 months ago to curb development throughout the county, putting three neighborhoods under a microscope to decide what they should look like as builders move in.

The first three "sector plans" will lay out blueprints for growth in Nokesville, a rural enclave in the county's western end, and two strips already heavy with commercial development--the intersections of Routes 1 and 123 near Occoquan and Interstate 66 and Route 29 in Gainesville.

The sector plans could map out anything from the shape of a streetlight to the size and use of a commercial building, county planners said.

"What this does is look at a small area with a finer lens," said Terry Rixse, a county planner.

The county hopes eventually to design as many as eight smaller, geographically based master plans. The idea is to lay out more detailed visions for growth than the more sweeping Comprehensive Plan passed by the Board of County Supervisors in August 1998.

The Comprehensive Plan, narrowly approved after a two-year debate, cut nearly 30,000 potential homes from county maps, sharply increased developers' fees and set aside about 80,000 acres in a "Rural Crescent" in western Prince William for farms and subdivisions with lots of 10 acres or more.

Supervisors will appoint 12-member panel of residents this week to map out the first three sector plans, work that is scheduled to start in October and conclude next summer with public hearings. The sector plans will then be incorporated into the larger growth plan.

Officially, the local plans are not designed to change an area's zoning to allow more intensive development. But some slow-growth activists fear they'll be vehicles for just that.

"You'll see dramatic changes in land-use categories that will include areas with much higher density," said Robert Moler, a longtime slow-growth activist who lives four miles from the I-66 and Route 29 interchange. Moler is also the campaign manager for Democrat Gary Friedman, who is running for the board as a slow-growth candidate in the Gainesville District against Republican incumbent Edgar S. Wilbourn III.

The 1,800-acre swath there and an additional 250 acres at Routes 1 and 123 will be ripe for economic development once major road projects are finished in both areas. A $70 million project to be designed in the next year aims to ease traffic from I-66 onto Route 29 and other roads and will depress railway tracks now in the middle of the interchange.

Construction of a new $30 million interchange at Routes 1 and 123 is scheduled to begin in a year and result in less stop-and-go traffic along Route 1.

The local plans could call for service roads and lay out what signs and buildings along the strips should look like. They may designate whether new commercial buildings should be large office complexes or mom-and-pop stores, for example.

"The idea is to plan things now, before the construction is finished," county Planning Director Rick Lawson said.

In Nokesville, the task is slightly different--how to preserve the area's small feel of a settlement without pushing out all development.

"There's a small-town atmosphere that should be cherished and preserved," said Elizabeth Cronauer, president of the Nokesville Civic Association and a member of the new citizens panel.

But the blueprint for Nokesville is likely to ignite a lively debate, because the county is preparing to bring sewer lines to the area to relieve some aging septic systems. Sewer lines would make the area attractive to developers.

Prince William eventually hopes to launch other small-scale growth plans in Bristow, around the county's landfill and government centers and in Brenstville, where preservationists are restoring a historic district.

"There are no hard and fast rules about how the [local plans] will proceed," said Supervisor Ruth T. Griggs (R-Occoquan). "It's kind of wide open, and that's what worries people."