It started last winter, before anybody was certain that John F. Herrity and Audrey Moore would be candidates for chairman of Fairfax County's Board of Supervisors. The opening volley was a four-page missive signed by Earle C. Williams, president of BDM International Inc. of Tysons Corner.

Although it never mentioned Moore by name, the letter's thrust was clear: "Voters will be deciding whether to continue the economic prosperity enjoyed under Jack Herrity, or to return to the myopic policies which in the early 1970s poisoned the county's image with the business sector . . . . "

Fairfax County's businessmen and developers, who wield enormous financial clout, have mobilized for the Nov. 3 election between Herrity, the Republican incumbent, and Moore, a Democrat of the Annandale District, as never before. Their goal is to avert what many business people think would be the catastrophe of an Audrey Moore administration.

Many of Moore's business critics have derided her proposals to come to grips with the county's transportation problems in part by slowing the rate of growth. They contend that Virginia's courts and legislature would never permit such an infringement on property rights. At the same time, they argue that most of the county's major development decisions have been made and that it is too late to reverse such trends.

If their contentions are true, why are the business and development communities convinced that Moore would make Fairfax less attractive to corporate America?

"The perception is this woman will do anything to right a wrong, and the wrong in her view is the unbridled development of the county," said Randall Byrnes, head of the Washington office of Spaulding & Slye, a developer of office buildings.

Responded Moore: "I'm very much sympathetic with the needs of the guy in business who is trying to make a living. I'm not a bureaucrat, never have been."

Moore's lack of support in the business community has translated into a large fund-raising advantage for Herrity. At a meeting this summer, some of the county's most prominent developers and business leaders agreed to raise $10,000 apiece for Herrity's campaign. Despite that advantage, Moore holds a lead of 7 percentage points among likely voters, according to a recent Washington Post poll.

Despite the substantial market forces in the Washington area that have contributed to Fairfax's growth and despite the state labor laws that make the county attractive to firms searching for an outpost near the nation's capital, many business leaders seem to view the county's thriving economy as a fragile achievement that could be upset easily by Moore and her slow-growth policies.

Byrnes cited Moore's repeated statements that she would appoint task forces to study development issues, saying:

"All the time that's required to study these things could take years, and that could be enough time to kill the goose that laid the golden egg. Businessmen hate uncertainty. Once they know the rules, then they can spend risk capital. But if they don't know the rules, that's a very, very distasteful situation to most businessmen."

In campaign appearances, Moore has pledged repeatedly to "phase in" changes in the regulations governing growth, to treat business leaders "fairly" and to include them in important county decisions. She says she intends to perpetuate the county's prosperity.

Moore has refused to detail the specific measures she would use to check development. She speaks of "moderation" and "managing" and "balancing" growth -- buzzwords that make developers cringe and fear the worst.

Despite her reluctance to spell out the specifics, Moore has given a few clues about the policies she might pursue if elected. For one, she is considered likely to renew a proposal, narrowly defeated last year, that would severely restrict the amount of office construction permitted on 10,000 acres of land zoned for industrial use around the county. The county board rejected the proposal last December by a 5-to-4 vote, with Moore voting in favor and Herrity opposed.

In addition, there is some speculation by county officials as well as developers that Moore may seek to broaden those proposed restrictions to cover land zoned for commercial uses as well.

Those kinds of rule changes -- called "downzonings" in the parlance of land-use lawyers and planners -- pose perhaps the greatest risk to the county's economic future, business leaders say. Even if they are struck down by state courts, the litigation can take months or years to be resolved and businessmen and developers can incur heavy costs in the process.

"Businesses can't afford to invest their future at the risk of having it pulled out from under them two years down the road," said Francis A. McDermott, a respected land-use lawyer who has represented a number of large corporations that moved to Fairfax. "I'm not saying {the downzonings} could be done successfully, but it throws you into an atmosphere of uncertainty and litigation. We don't need that."

McDermott and others say that firms such as Electronic Data Systems Corp., the Texas-based computer company that plans to build a regional center that would employ 3,000 people in western Fairfax near Dulles International Airport, might not select the county if their expansion plans are jeopardized by changes in zoning rules or litigation involving the county government.

Simply by appointing panels to study decisions such as the expansion of a sewage plant, or by administrative actions such as the review of building inspection policies, Moore could delay building plans, erode developers' profits and undermine corporations' confidence in Fairfax as a place to do business, corporate leaders and developers maintain.

Some say that the wariness with which many business leaders view Moore has less to do with her plans for slowing development than with her lack of private sector experience.

While Herrity has been in business for himself since 1969 -- he owns a small insurance agency in Fairfax City -- Moore has never had her own business and held just one job in the private sector, from 1950 to 1955, for a Washington lobbyist. She married a civil servant.

"Audrey is from a fairly well-to-do background where everything was provided for," said one developer who asked not to be identified. "Everything was provided for by the big security blanket of the government and as far as she's concerned, all these things happen automatically -- roads and schools and so forth.

"Business people {on the other hand} have constantly to risk what they've built up in order to keep their business going. But when you work for the government you never have to do that, and you'll never have a set of circumstances that will reduce your standard of living very much."

Moore pointed out that her father had his own export business, insisting, "I'm very much attuned to people in the private sector."