Fairfax County Board Chairman John F. Herrity won an easy and overwhelming victory over his two opponents yesterday in the Republican primary in Virginia's 8th Congressional District.

With all of the district's 145 precincts reporting, Herrity had won over 52 percent of the vote and will face two-term Democratic incumbent Rep. Herbert E. Harris - Herrity's one-time nemesis on the Fairfax County board - in next fall's congressional election.

In addition, voters in Fairfax County decisively rejected $16 million in bonds that would have been used to build new storm drainage facilities and fire stations.

Herrity won handily in southern Fairfax County, which contains Springfield, the magisterial district he once represented on the board and an area that accounts for 60 percent of the registered voters in the congressional district. He also won over 50 percent of the vote in Alexandria, and carried the city of Manassas and northern Stafford County as well.

Herrity's closest contender for the nomination was Robert L. Thoburn, a first term General Assembly delegate and a Presbyterian minister, who had come within a shadow of winning the party nomination two years ago.

This time, Thoburn managed to garner only 30 percent of the vote, carrying Prince William County, and Manassas Park's single precinct.

Del. Robert E. Harris trailed far behind with a little more than 17 percent of the vote.

Herrity attributed his victory to his campaign organization's ability to get his voters to the polls and said that the major issue in the fall campaign was going to be the federal deficit.

In addition, Herrity pointed to the recent success of Proposition 13 in California, a measure that drastically cuts that state's property taxes. "Proposition 13 is as much a mood and an attitude as it is a specific," Herrity said. "I think that kind of concern is as prevalent here."

But Herrity did not blame the defeat of the two Fairfax County bond issues on Proposition 13 sentiment. "I told the board it was a mistake to have a bond referendum in a Republican primary," Herrity said. "Republicans just don't vote for bonds that often."

Thoburn, in fact, pointed to the bond issue in explaining his own defeat. "They defeated the bond issues in Fairfax but selected the candidate who supported them," he said. "I think my own strategic error was in agreeing not to attack the other candidates. The voters just didn't understand our differences on the issues."

Herrity said he plans to remain chairman of the Board of Supervisors while he campaigns for Congress, as did Herbert Harris when he took the seat away from Republican Stanford Parris in 1974.

The complete, unofficial totals in the 8th district showed Herrity with 9,341 votes, compared to 5,457 for Thoburn and 3,923 for Robert Harris.

The voter turnout, unusually sparse even for a primary campaign, was blamed not only on an early morning rain but on the campaign itself, which never reached the level of flamboyance many had expected of the candidates.

From the beginning, Harris, Herrity and Thoburn had pledged themselves to a "gentlemen's agreement" only to attack each other in the interest of party unity. They agreed that inflation was the No. 1 issue and Rep. Harris the No. 1 enemy.

In public, the three candidates put the finishing touches on their individual portraits of the incumbent Harris as a big spending liberal, but it was behind the scenes that the campaigns really coalesced. Using the sophisticated and expensive political techniques of direct mailings, telephone banks and private polls, each candidate tried to identify his supporters and urged them to the polls.

By the end of the campaign, both Thoburn and Harris were trying to draw the distinctions between their candidacies more dramatically, offering detailed reviews of each other's vote-getting potential and speaking styles. Herrity, however, remained aloof from the last-minute volleys, stressing party unity in the fall.

Despite the lack of attention the race received from the voters, it was seen by many Republican partisans as a barometer that would help to determine on which end of the ideological spectrum Northern Virginia Republicans would focus their future efforts.

Northern Virginia delegates to the Republic Party convention early this month tended to support moderates Linwood Holton and John Warner for the Senate nomination that finally went to conservative Richard Obenshain. Thoburn, and Harris, however, said throughout the campaign that most Northern Virginia Republicans are conservative.