The Fairfax Country Board of Supervisors approved rezoning for 271 houses yesterday, accepting the developer's plans to employ construction practices designed to prevent storm water runoff that would pollute the Occoquan Reservoir, the drinking water supply for more than 600,000 Northern Virginians.

The antirunoff techniques could become a model for developers in the Occuquan Basin, according to proponents.

Nevertheless, the rezoning was opposed by the Upper Occoquan Sewage Authority, which operates an $82 million sewage treatment plant near the construction site. Opponents have argued that the antirunoff practices are unproved.

The vote approving the rezoning for single-family homes and town houses planned by Trifam Systems Inc. on a 45-acre site at Compton and Old Centreville roads was 8 to 1, with Supervisor Audrey Moore (D-Annandale) in the minority.

The owners have agreed to spend $80,000 on what water experts call "best management practices" to control runoff, which has been identified as perhaps the worst form of pollution affecting the Occoquan.

In approving the rezoning, several supervisors said they were in no way bowing to a threat that the owners plan to sue if the rezoning was denied.

E. A. Prichard, an attorney for the owner, sent Supervisor Marie Travesky (R-Springfield), in whose district the land is located, a letter stating that his clients planned to sue the country if the rezoning was denied. Prichard said the letter was not a threat, but "an attempt to summarize a lengthy record."