A sewer extension proposed to benefit George Mason University's ambitious expansion plans was unanimously endorsed last night by the Fairfax Country Board of Supervisors.

The supervisors rejected a proposal by country planners to extend sewer lines to land adjacent to the campus. Some of that land is owned by John T. Hazel Jr., a developer, zoning lawyer and a member of the university's Board of Visitors.

The approved sewer extension will serve a 200-acre West Campus, now mostly forest. George Mason planners foresee an athletic complex with a field house there, as well as buildings that could house professional schools.

"In supporting a sewer expansion program for the university alone, I believe . . . we are maintaining our responsibility in ensuring that George Mason reaches its potential to become a great institution," said John F. Herrity (R), supervisors' board chairman.

The proposal to extend sewerage to serve the university alone, which would cost $292,500, now goes to the State Water Control Board for approval. The plan calls for the university to assume full cost of a $135,000 pumping station and pay $157,500 for sewer mains.

The rejected proposal would have cost $589,797, with the cost shared by the university and private landowners and developers.

Hazel owns a 50-acre tract near the university's West Campus land; extension of sewerage is essential for that land's development into a 99-lot subdivision called North Farm.

Hazel had said "it's not a case of development or no development," since he could redesign the subdivision for septic service by losing about 10 lots.

Supervisor Adreyy Moore (D-Annandale), a slow growth advocate and frequent adversary of Hazel, said the sewer proposal smacked of conflict of interest and would open a long-protected, enviromentally fragile area to high density development.

Moore objected last night, saying that if the sewer were extended to the university alone, it "could still be legally tapped later by anyone who owned land in the area" and that it would be capable of sewering "10,000 households."

The approved plan contains a provision specifying the sewer is for university use only.

Country Attorney Frederick Lee Ruck said private land owners could not tap the university's sewer.