Fairfax County Board Chairman John F. Herrity, trounced a month ago in Northern Virginia's most expensive local political race ever, is $25,000 in debt to his campaign creditors while Chairman-Elect Audrey Moore's campaign, boosted by a small army of last-minute contributors, is running a surplus.

Financial reports filed yesterday showed that the two candidates, along with a pair of independents, spent about $1 million in their race for the county's top elected job -- a sum that has prompted calls from Virginia Gov. Gerald L. Baliles and others in the state to tighten the rules governing campaign finances.

In Northern Virginia's most visible and highest-stakes race, perhaps the biggest surprise to many analysts (and Moore's own aides) was her ability to amass big-league money from thousands of donors who wrote relatively small checks.

When Moore's campaign got under way last spring, David G. Russell, her treasurer, estimated that she would have to raise $125,000 to $130,000 to have a shot at beating Herrity, who has held the job since 1976.

The forms filed yesterday showed that Moore raised nearly $328,000, or more than twice Russell's projection, from more than 5,600 contributors. A large chunk of that sum -- about $70,000 from almost 1,000 donors -- was received in response to a fund-raising letter sent to Moore loyalists just before Election Day. The campaign is running a surplus of about $8,700.

"We never envisioned that we would raise as much as we did, and it was all in small contributions," Russell said. "It came as much as a surprise to me as it did to everybody else. It really opened my eyes up."

Herrity's campaign fund raising, on the other hand, neither exceeded nor fell short of its projections. Herrity campaign officials had predicted they would raise $500,000 or more. The reports filed yesterday showed about $521,000 in contributions. The report also listed debts of about $32,000 and about $6,900 in cash on hand for a net debt of approximately $25,000.

Herrity had substantially fewer contributors than Moore. The precise figure of contributors was not available yesterday.

Herrity campaign chairman William J. Madden Jr. said Herrity's debt is no greater than in past campaigns as a proportion of his total campaign spending. "Jack intends to pull together all the bills we owe and put together whatever's necessary to pay them off," Madden said. He said Herrity will probably hold a fund-raiser to meet the outstanding obligations.

Campaign spending in this year's races for state and local offices was sharply higher than in previous elections, a jump that caught many politicians by surprise. In 1983, for example, the last time Fairfax voted for the county chairmanship, Republican Herrity and his Democratic opponent spent barely $100,000 -- a tenth of this year's outlay.

While Herrity-Moore was the most expensive contest in Fairfax this year, several other races for county supervisor cost more than $100,000.

The most expensive Northern Virginia contest for the state legislature was waged by state Sen. Clive L. DuVal 2d (D-McLean) and Republican challenger Bobbie Kilberg, who spent a total of about $335,000, split more or less evenly between them. DuVal won.

The costliest race in the state was between state Sen. William F. Parkerson Jr., a Richmond area Democrat and the Senate's most senior member, and Edwina (Eddy) Dalton, a Republican who is the widow of former governor John Dalton. The two spent well over $1 million. Dalton won.

Larry Sabato, an associate professor of government at the University of Virginia and an authority on Virginia politics, wrote in Sunday's Washington Post that preliminary figures show that the average candidate running in a contested race for the House of Delegates spent more than $43,000 and the average contested state Senate candidate spent $175,000. Compared with 1983, Sabato said, the figures represent increases of 150 percent for House candidates and 350 percent for Senate candidates.

Virginia has no limits on donations or spending in state and local races.

Sabato and other analysts, pointing to the two-thirds of Virginia's incumbent legislators who were unopposed by the other party this year, fear that the soaring cost of running for office is discouraging qualified candidates.

Paradoxically, spending limits -- if they can be drawn in conformance with the Constitution -- are generally considered an advantage to incumbents, who do not have to spend as much to get their names known.

In a news conference the day after the elections, Baliles called 1988 "the first, best opportunity to restore some common sense" to campaign finance rules.

Lawmakers may not see it that way. Senate Majority Leader Hunter B. Andrews (D-Hampton) said in an interview yesterday that he favored a study of the issue of limiting spending and donations. "I just don't think you can resolve that in this {1988} session," he said. "I have problems with any caps because of the way people get around them. All you have to do is look at the federal laws," which have been criticized as easy to evade.

Andrews said he supports legislation that would require state parties to disclose names of those who specified which candidates would get their contributions.