The Fairfax County Board of Supervisors, handing a modest victory to advocates of controlled growth, voted unanimously last night to consider limits on development in rural western Fairfax before granting lucrative development rights to landowners in a strategic corner of that region.

One hundred square miles of farms, woods and estates--a quarter of the county--are at stake as the board decides the future of what has been called Fairfax's last frontier. Two citizen commissions recently issued recommendations that differ sharply in philosophy, one urging strict limits on growth throughout the region and the other pushing urban-style development in 5,000 acres of the quadrant at the intersection of Rte. 50 and Interstate 66.

The board voted yesterday not to approve the intense development at I-66-Rte. 50, which would greatly enhance land values there, before acting on the overall plan to limit growth, which many of the county's politically powerful builders, developers and landowners oppose.

"If we deal with 50-66 first, some of the interests of some of our board members would drop off very quickly," said Supervisor Martha V. Pennino. "It's a way of holding their feet to the fire, if you will."

Fairfax has tried before to limit growth, but retreated in the face of political protests or reversals in court. This time the supervisors believe they can justify their plan, despite Virginia judges' traditional respect for property rights, by pointing to the region's endangered water supply.

Most of western Fairfax slopes toward the Occoquan River, which provides drinking water to Alexandria and much of Fairfax and Prince William counties. A citizens task force on the Occoquan said that without controls prohibiting anyone from building a house on less than five acres the river will soon become polluted.

Some supervisors last month questioned whether Fairfax should control its growth when parts of Prince William, Fauquier and Loudoun also drain into the Occoquan. But the county staff said Fairfax is likely to develop first.

"Our 17 percent of the Occoquan watershed is where the growth is right now," said Supervisor Thomas M. Davis III. "If we don't set the example right now, I think we're going to be very hard pressed 10 or 20 years from now to tell them what to do."

The citizens commission on the Rte. 50-I-66 area recommended that the supervisors encourage the construction of offices, stores and industry around the Fair Oaks Mall and the proposed county governmental site. J. Hamilton Lambert, the appointed county executive, lobbied during the past few weeks to convince supervisors that development at 50-66, which is partly in the Occoquan watershed, should hinge on reduced development elsewhere.

"This isn't the old, traditional antigrowth thing," Lambert said. "What you're doing is transferring density to where it should be and then downzoning to protect the reservoir and partially offset the growth."

Supervisor Audrey Moore, who has said that the citizens task force was dominated by developers and landowners with a direct stake in the outcome, said the plan offers too much density without specifically requiring developers to pay for the roads and other facilities that would be needed. Board Chairman John F. Herrity said the plan will ensure that Fairfax attracts the jobs and tax base it needs.

Both plans will be considered at public hearings during the next three months, with the board scheduled to act in late July.