Virginia Gov. Gerald L. Baliles gave Audrey Moore, the Democratic candidate for the chairmanship of the Fairfax County Board of Supervisors, a major boost last night by throwing his support to her campaign.

She is challenging Republican Board Chairman John F. Herrity in the Nov. 3 election.

Even though Baliles is a Democrat, many had speculated as to whether the governor would align himself with Moore and if he did, how closely.

Baliles, who is popular with the business community, has traveled widely to promote Virginia's economic development. Many Fairfax County business leaders are strongly behind Herrity and fear that Moore is antigrowth.

Last night at a pig roast fund-raiser near Fair Oaks Mall, Baliles made his support clear: "We both recognize that economic vitality sustains our county and provides revenue . . . . I can work with her." He continued, "I'm here to say without equivocation that Audrey Moore should be the next chairman of the Fairfax County Board of Supervisors."

Calling Moore, "honest, reliable and trustworthy," Baliles said, "She's a friend. When it counted, she was there for me."

Moore was instrumental in turning out the vote for Baliles in 1985, especially in Annandale, the district she has represented on the Board of Supervisors since 1972 and an area that was seen as crucial to Baliles' bid for the Democratic nomination.

Moore said it was unfair to describe her as antigrowth. "I am not against development, per se," she told the crowd of 200 last night, saying she was against the way it has been managed and planned.

Earlier in the day, Moore said: "I know what is being said, that Jerry {Baliles} and I stand for different things. We don't. Jerry's for planning. He wants to upgrade the economy and bring business into the state . . . . I'm not against business."

Moore's campaign advisers announced last night that they had raised enough money to air radio and television advertisements. Moore has raised at least $165,000, about half as much as Herrity.