The Fairfax County Board of Supervisors yesterday approved a controversial plan to barricade four streets in the western part of Great Falls to keep out commuters from neighboring Loudoun County.

The board also approved the expansion or construction of two short roadways to ensure that most of the additional traffic from growing Loudoun developments is dumped onto Route 7 in Loudoun, not in Fairfax County.

The actions are expected to touch off a border battle between the two counties, as the wealthier, less developed Great Falls tries to protect itself from traffic generated by the rapid growth anticipated in Loudoun.

Loudoun County officials have strongly protested the plan, which was drafted by Supervisor Nancy Falck, a Republican who represents the adjacent Dranesville area.

Great Falls residents of Thomas Avenue, the street that would be most disrupted by the plan, are also upset over the proposal, which would erect a gate to split their road in half. One resident, Phyllis Marshall, called the gate "the equivalent of the Berlin Wall, or perhaps better would be the Falck Wall."

But residents of other areas of western Great Falls, where most lots range from two to five acres, have complained bitterly that traffic from Sugarland Run, Sterling Park and future Loudoun County developments will flood their streets, which were designed only for limited traffic.

Estimates vary but most planners anticipate that the projected growth will mean at least 24,000 more cars on the roads every day.

Loudoun had planned to build a roadway, known as the Route 28 Loop Road, to connect the growing subdivisions with Route 7, but lacks the money to proceed.

In an effort to force Loudoun to deal with the problem, Falck developed a plan to construct cul-de-sacs on Kentland Drive, Brockman Lane and Plantation Drive, at the county border. The Thomas Avenue split would come near the Fairfax County Water Authority easement. The eastern half of the street would be a deadend. The western half would be converted to a four-lane roadway, which would extend northward from the Fairfax County Water Authority easement to the county border.

Supervisor Marie Travesky, Republican from the Springfield District, noted that Falck is going to get criticism for anything short of the Route 28 Loop Road solution, but that the plan approved by the board would at least "minimize the negative impact on Fairfax County communities."