Robert L. Thoburn, a Christian educator and former Republican state legislator from Fairfax, yesterday lost his bid to build a Christian school for 480 students in a residential neighborhood north of Fairfax City.

Thoburn's application to build the school in a thickly wooded section of Oakton was defeated on a tie vote by the Fairfax County Board of Supervisors. The vote was 4 to 4, with Supervisor Joseph Alexander absent. Alexander said earlier he would have abstained on the vote because he was not present for a public hearing on the school a month ago.

The board also rejected a related application by Thoburn to build 17 homes on property adjoining the site of the proposed school.

Thoburn's application was opposed by most residents of the Oakton community but supported by parents whose children have attended his Fairfax Christian School, which now rents space in two Baptist churches south of Fairfax City.

After the vote, Thoburn blamed the defeat on what he called the liberals on the county board. "It's an attack upon Christianity," he declared. "It's like the Soviet Union. They allow religious freedom, they say, but they zone people out."

His son, John M. Thoburn, a partner in his father's businesses, added: "They don't like our political philosophy and our religious teaching. It's absurd."

Despite the Thoburns' charge that the decision on the school turned on political issues, Supervisor James M. Scott, a Democrat whose district includes the Oakton area, insisted that the board considered land-use issues paramount.

Scott, citing the county staff's recommendation that the Thoburn application be turned down, voted against the school. He said it did not conform to the county's master plan, which calls for single-family homes on large parcels in the area around Thoburn's land.

Scott said that Thoburn had made concessions to the county in the course of negotiations on the school, including cutting the size of the student body by about 100, but that these changes were "minor in relation to the requirements of the comprehensive plan and the zoning ordinance."

Thoburn founded the Fairfax Christian School in 1961, and until last year it was located on Pope's Head Road south of Fairfax City. Last year, the Saudi Arabian Embassy paid him $3 million for the school's old campus, and Thoburn moved into rented quarters in two Baptist churches on Ox Road south of Fairfax City.

Thoburn vowed to fight the board's decision yesterday. "We intend to come back on this," he said. "We intend to take this to court."

His son pledged: "We want to put a school there and we definitely are going to do that. It's an absurdity not to allow a school there."

Robert Thoburn said he would buy other properties around the county and build more branches of the Fairfax Christian School on them.

Voting for the Thoburn application were Chairman John F. Herrity, and Supervisors Thomas M. Davis III, Elaine McConnell, and T. Farrell Egge, all Republicans.

Voting against were Supervisors Martha V. Pennino, Audrey Moore and James M. Scott, all Democrats, and Nancy K. Falck, a Republican.