The Loudoun County Board of Supervisors Tuesday approved the rezoning for the massive Brambleton development just west of Dulles International Airport, authorizing 4,240 houses and millions of square feet of industrial and commercial space.

The supervisors also voted 4 to 3 to approve a statement on the proposed western bypass to the Capital Beltway that calls for the consultant to give further study to potential locations for the hotly debated highway.

Brambleton, proposed by the Vienna-based Kettler & Scott, was approved 5 to 2, with Supervisors Betsey Brown (D-Catoctin) and Thomas Dodson (D-Mercer) opposing the application. Board member Steve Stockman (R-Broad Run) was absent.

Brambleton, to be built between the Beaverdam Reservoir and the village of Arcola along Belmont Road (Route 659), will feature a town center and a variety of house styles that will be affected by aircraft noise. The developers have agreed to inform potential buyers of the proximity of the airport.

County staff and some county board members pointed out that the developers, who also are building the huge Cascades project in eastern Loudoun County, have exceeded most existing county government guidelines concerning promised road improvements and other amenities. Such contributions, called proffers, are voluntary under state law.

However, some county board members said those guidelines are inadequate. Officials said that the county could be short more than $10 million over two decades in funds needed to develop the road network near Brambleton. Brown and Dodson cited traffic problems in voting against the application, saying that the project and other expected developments could overwhelm Route 50.

Supervisor Ann Kavanagh (D-Dulles), who made the motion to approve Brambleton, said that three years ago she advised Kettler & Scott that the plans would be approved "over my dead body." She said she changed her mind because the developer made "a number of significant changes," including designating 300 units "affordable housing" and 300 units for the elderly.

In other business, the board, approving a formal statement to be included in testimony on the western bypass, accepted a substitute to a draft favored by Board Chairman Betty Tatum (D-Guilford District) and Vice Chairman Charles Bos (D-Leesburg District). Their original proposal, backed by Kavanagh, listed detailed objections to all three suggested routes through the county.

Eastern Loudoun Supervisor Howard P. Smith (D-Sterling) joined three board members from western Loudoun in pushing through a shorter statement that emphasizes opposition to "the use of Route 15 as a de facto western bypass" and calls for further study of a bypass route with few interchanges in Loudoun.

State highway officials have suggested that Route 15, a crowded north-south artery, will be at least six lanes wide in a decade or two whether or not parts of it become the location for the western bypass.

Tatum said the statement supported by the board majority is too vague, adding that funds for any additional study by the Vienna-based consulting firm of Bellomo-McGee will come out of the county's limited allocation for primary road construction.

The approved statement was endorsed by Friends of Route 15, the Piedmont Environmental Council and the Washington Airports Task Force.