Fairfax County Republicans, long torn by bitter ideological feuds, have apparently ousted conservative party chairman Benton K. Partin, who in four years at the helm of the GOP has embittered moderates and allied the party with religious groups and the "New Right."

In his place, county Republicans seem on the verge of installing James D. Swinson, an unabashed, 73-year-old country boy who served as sheriff for 16 years before he retired in 1980.

In voting around the county Monday night to choose delegates to the Fairfax Republican convention next month, Swinson amassed 271 delegate votes to Partin's 237. Although those figures could change by the April 12 convention, they seemed to signal an impending change in leadership and direction of the GOP in Virginia's largest and richest locality.

Swinson, a jovial, rotund man who describes himself as "a tough old goat," called on Partin to concede and avoid a bitter preconvention fight that could further divide the party.

"To put it in plain language, when you're beat, you're beat," said Swinson. "And by God he's beat. I'm hoping that [Partin] will join me in attempting to get the party back together. Let's forgive and forget."

Partin, 60, who has said Swinson would be an "embarrassment" and "disaster" as chairman, refused to bow out. He promised he will change the minds of some Swinson delegates before the convention. "That's not a big lead."

Swinson's candidacy and apparent victory amount to a revolt by the county's elected Republican officeholders against the party's right-wing leadership. All but a handful of Republican supervisors and state legislators from Fairfax are backing Swinson, who was one of the few GOP officeholders in the county in the 1960s and 1970s.

Partin has attacked elected Republicans behind Swinson's campaign, particularly county supervisors Nancy K. Falck of Dranesville District and Thomas M. Davis III of Mason District. He charges that they wanted to run the party on their own, recruited Swinson as a figurehead and pressured wealthy Fairfax builders to contribute to Swinson's campaign.

Swinson, who has raised about $15,000 in the race, has outspent Partin by at least 5 to 1.

Swinson, Falck and Davis all deny Partin's accusations. Swinson's candidacy, they say, represents an effort to broaden the Republican Party base to include all factions.

Partin's quarrel with Fairfax's elected Republicans goes back at least to 1984, when he moved to exclude moderates from district and state GOP conventions. Despite Partin's later conciliatory language, the action enraged Republican county supervisors and state legislators.

In his two terms as chairman, Partin has repeatedly refused to appoint supporters of elected officials to key positions in the party hierarchy, insisting instead upon representatives of what he calls the GOP's "grass roots."

Elected officials have said that Partin's thrust has been to impose ideological tests, promoting those who toed the line and excluding dissenters.

The Democratic sweep of the three statewide elections last November, in which Republican gubernatorial candidate Wyatt B. Durrette was defeated in his home county of Fairfax, led many GOP officials to acknowledge the party had veered too far to the right.

But Partin's supporters said he is being made a scapegoat. "The difficulties the Republicans experienced last year were statewide," said Lawrence D. Pratt, executive director of the Gun Owners of America and a close associate of Partin. "I think the party has done very well the way it is. If it ain't broke, don't fix it."

The contest between Partin and Swinson will now shift to organizational battles. Both camps will attempt to dislodge the other's delegates in the remaining month before the convention and both will be faced with making sure as many of their delegates as possible actually attend the convention.

Once the party chairmanship is settled, the county GOP will turn to the fall elections in Virginia's 8th and 10th congressional districts. In the 8th District, Rep. Stan Parris is thought to stand a good chance of defeating whoever wins the Democratic primary scheduled for June 10. Four Democrats who have never held public office are considering entering the race. In the 10th District, Rep. Frank Wolf faces a tougher race against former Arlington County Board chairman John Milliken.