Zoning attorney Marc E. Bettius has sued Fairfax County a number of times on behalf of developers. But Bettius is so angry at one developer who has sued Fairfax that he has become the county's cocounsel.

"There comes a time when a developer overreaches," Bettius said, "and when he does, somebody has to come in and put a stop to it."

What has made Bettius mad is that United Developers Housing Corp. is trying to undercut the routine horse-trading that goes on between developers and the county supervisors over zoning cases. United Developers gave the county two school sites in the Oakton Village complex in 1966 in exchange for higher-density zoning and now is trying to renege on the pact and get the land back. The firm claims the agreement "was obtained under duress as a result of improper coercoin by the Board of Supervisors."

"We're all big people," said Bettius, who has no connection with United Developers. "If I commit myself to something, I better be prepared to stand behind my commitment. This case is pivotal. It will be crucial to my ability to stand up before the Board of Supervisors and say I will deliver what I promise."

If United Developers wins and recovers the two sites, totaling about 14 acres, it would have a windfall of $500,000 or more.

A victory for the developer would also cast doubt on legality of other horsetrading on rezoning cases between the supervisors and developers. It has become a common practice for developers who want special zoning - like that at Oakton Village - to give in exchange some land for schools, parks or other public facilities.

United Developers' suit against Fairfax has created amazement in the small but powerful community of lawyers who specialize in zoning cases.

Grayson P. Hanes, a partner with John T. Hazel Jr. (probably the most influential zoning lawyer in the county), dropped United Developers as a client when the firm said it would go to court in an attempt to get school sites back.

Hanes, because of his former connection and the possibility he will be called as a witness by the county, declined to discuss the case.

His partner, Hazel, said, "I think it is fallacious and inappropriate for them (United Developers) to claim duress . . . I hope they lose."

United Developers is headed by Charles E. Taylor and C. Daniel Clemente, who are partners in another Fairfax law firm, Taylor and Clemente.

Taylor and Clemente are involved in the Oakton Village project in several ways. They head United Developers, which owns the condominiums and vacant land. VNB Mortgage Corp., which provides loans to condominium buyers, is a subsidiary of Virginia National Bank, which holds $11 million worth of notes from United Developers. The circle is closed when Taylor and Clemente serve as settlement attorneys for the purchasers of condominiums they have sold.

Repeated attempts to reach Taylor and Clemente were unsuccessful.

To wage its fight against Fairfax, United Developers went to the high-powered Washington law firm of Hogan & Hartson. Before the suit was filed, Hogan & Hartson partner and former Virginia Republican Gov. Linwood Holton visited Fairfax Board Chairman John F. Herrity, also a republican, to ask if the supervisors couldn't be persuaded to give the school sites back to United Developers.

When Herrity, the rest of the board and County Attorney F. Lee Ruck balked, another lawyer from Hogan & Hartson was brought in for the court battle. He happened to M. Langhorne Keith, Ruck's predecessor as county attorney.

Keith would not comment on the case, but when asked about the practice of developers dedicating school sites, he said, "Developers do it because it's the way to get a zoning. They (the supervisors) put a gun to your head."

Not surprisingly, Assistant County Attorney Robert F. Flinn, who will team up with Bettius for Fairfax, saw things differently.

"Nobody says you have to do it," he said. "The zoning ordinance says, if you want to do it, here are the goodies (higher densities) you'll get. They (the developer) came in and begged for the zoning."

United Developers is actually one of the successor owners of the Oakton Village property, and wasn't in existence when the school-site agreement was made, a point made by Flinn in his answer to the firm's complaint filed in Fairfax Circuit Court.

Jeffrey Sneider, who owned the property before United Developers, (he went out of business when his firm failed), said that when he bought the land, he knew 14 acres would have to be given to the county. "I bought it with my eyes open," he said.

However, Sneider said there is a surplus of school sites in the county. "The land is sitting fallow, there are no taxes paid on it, the public gains no benefits," he said.

Although the Fairfax School Board requested the two sites in 1966, when the zoning application was submitted, the downward trend in births has eased the demand for new schools. As a result, the school board has declared one of the two sites surplus property.