Fairfax County Board Chairman John F. Herrity, who this summer persuaded some of the county's preeminent developers and business leaders to raise $10,000 apiece for his reelection campaign, has outraised and outspent Supervisor Audrey Moore, his chief opponent, by nearly 2 to 1 since mid-August, according to financial reports filed yesterday.

Herrity, a Republican struggling to win a fourth term as the county's top elected official, has collected about $295,000 since Aug. 11, bringing total contributions to his campaign to about $468,000, the reports said.

Moore, a Democrat who never ran countywide before this year, raised about $165,000 in the same period, raising her donations to about $275,000, according to the financial statements. Moore and her aides have said they have not asked developers for fund-raising help.

The reports show that an independent candidate for the board chairmanship, James S. Morris Jr., has borrowed and spent about $90,000 to finance his campaign; another independent, R. Terry Robarge, has spent about $2,200, about half of it borrowed.

By Election Day next Tuesday, total spending for the board chairmanship, a largely ceremonial post that will pay a salary of $35,000 in 1988, is expected to reach $1 million. In 1983, the last time elections for the county's Board of Supervisors were held, Herrity and his Democratic opponent together spent barely $100,000.

Herrity's fund raising was apparently boosted by a meeting he held July 30 in which several of the county's best known developers, including John T. (Til) Hazel Jr., agreed to solicit funds on Herrity's behalf. Herrity had said earlier that he would not accept financial contributions from developers. Accepting their fund-raising help did not violate that self-imposed policy, he said.

Among Herrity's largest donations: $22,000 from the Virginia Republican Party; $11,000 from the Global Leasing Co. of Washington; $10,000 from the Heavy Construction Contractors Association, a political action committee, and $5,000 from IDC Drilling Co. of Arlington.

Among Moore's largest donations: $4,935 in printing services donated by Lee Graphics, a Lorton printing firm; $2,000 from Linda M. and Norma C. Hardee, described as McLean homemakers, and $2,500 from the Underdog Fund, a Democratic political action committee organized by Virginia Lt. Gov. L. Douglas Wilder.

No limits are placed on campaign contributions in Virginia, and corporate contributions are permitted.

Fund raising and spending for the other seats on the nine-member Board of Supervisors have also outstripped previous years. According to the reports filed yesterday:In northern Fairfax's Dranesville District, a three-way race that is by far the most expensive district contest, the candidates have spent or borrowed more than $200,000.

Supervisor Nancy Falck, the Republican incumbent, has raised $106,000, including $10,000 from the Virginia Republican Party. Lilla D. Richards, the Democratic challenger, has raised about $55,000. An independent candidate, Robert Thoburn, has borrowed about $45,000 from himself for the campaign.In a hard-fought race in southern Fairfax's Mount Vernon District, Supervisor T. Farrell Egge, the Republican incumbent, has raised nearly $83,000, including a $19,000 donation from the Virginia Republican Party. Democratic challenger Gerald W. Hyland reported having raised about $48,000. In western Fairfax's Centreville District, Democratic Supervisor Martha V. Pennino has raised about $65,000. Republican challenger Linda Douglas, aided by a $10,000 donation from the Fairfax Republican Committee, reported raising about $54,000.In central Fairfax's Annandale District, the only one without an incumbent in the race, Republican Pat Mullins raised about $61,000, including $9,800 from the Fairfax GOP committee. Democrat Sharon Bulova reported raising about $18,200, plus a $5,000 loan.In southwestern Fairfax's Springfield District, Republican Supervisor Elaine McConnell reported $42,000 in contributions, including $13,000 from the county GOP and $5,000 from the state GOP. Toni Carney, the Democratic challenger, raised about $8,900, not including a loan of about $4,500. Independent Thomas Giska did not file a report.In the central Fairfax Providence District, Democratic Supervisor Kate Hanley reported raising about $24,800. Her Republican challenger, Myron Smith, reported contributions of $13,100.

Supervisor Joseph Alexander (D-Lee) has no opponent, and in the Mason District the opponent of Supervisor Thomas M. Davis III, independent Daniel Belsole, did not file a report.

In Northern Virginia's most expensive and hardest-fought race for the state legislature, Democratic state Sen. Clive L. DuVal 2d has raised $147,000 and his Republican challenger, Bobbie Kilberg raised about $153,000.