The Prince William Board of Supervisors is expected this week to approve a controversial rezoning request that would create a 74-unit equestrian community on 198 acres in Gainesville. The board deferred action on the project for a week to study the development's impact on the area's water supply and to give developer John Marsh an opportunity to amend his plan to include off-site road improvements.

The deferment came at the request of Gainesville Supervisor Tony Guiffre, who said he shared the concern of residents that any new development in the Catharpin Road area, which is served exclusively by wells and septic systems, could cause serious problems with the water supply. All public hearings on the issue have been well attended by homeowners, especially those represented by the citizens advisory committee and UNFAIR (United Neighors Fighting Against Irresponsible Rezoning), although only a few were present at last week's board meeting.

The Planning Commision and the planning staff recommended approval of the development with a strong recommendation that Marsh construct a centralized water system that would eventually fall under the ownership of the Prince William County Service Authority. The authority had said that, because the project would be on the public sewer system, it should have public water as well.

The developer has promised either to dig 74 individual wells or to develop a public water system for the project, which would include a farm for the stabling and training of local horses. According to Guiffre, the public water line can be extended under Interstate 66 to Catharpin Road.

"We do have ample water in this county," he said. "The centralized system should be built to eliminate potential problems." The supervisor said the fact that the development is low-density -- under the current zoning ordinance Marsh could have requested up to 240 units -- has made the project easier for everybody, including its opponents, to accept.

"With such low density we won't have to build a high school," he said. "This community can be an asset to the county. But the water in the ground belongs to everybody, and just because you have the longest straw doesn't mean you should get all of it."

In other business, the board approved a Coles District rezoning that brought more than 100 people to protest the shopping center on Rte. 234 and Counselor Road that the rezoning would allow. The board action drew promises from members of the Woodbine Civic Association that they would not patronize the center. The Planning Commission had recommended that the request be denied. "It's always difficult to go against a large number of citizens," Guiffre said later. "But if we don't have a solid reason for denial, we end up in court. And we'd lose."

The board also appropriated $21,908 from the emergency reserve fund for two positions necessary to administer the recently approved cable TV ordinance. The new employes, one part-time and one full-time, will work out of the consumer affairs office. Their duties will include reviewing and processing licensing applications, making recommendations to the board, reporting on resolved complaints and drafting amendments to the new code.

In addition, the supervisors approved $50,000, also from the emergency reserve fund, to complete installation of street lights through 1985. According to a spokesman for the county finance office, the cost of installation has increased over the past several years, particularly in subdivisions with underground wiring. Additional costs are incurred when easement acquisitions are required, the spokesman said.