Virginia Republican gubernatorial candidate Wyatt B. Durrette scored a key tactical victory on the Fairfax County home turf of his opponent, Rep. Stan Parris, last night, dealing a potentially crippling blow to Parris' efforts to revive his struggling campaign.

In a contest considered crucial, Durrette's forces blocked a move by Parris to lock up all 526 Fairfax delegate votes -- one-fourth of those needed for nomination at the party's May 31 convention in Norfolk.

Durrette, 46, stopping short of claiming a victory in his six-month battle with Parris, said, "we have more work to do." But his press secretary, Don Harrison, said, "we are over the top." He said that by stopping Parris' move, "that's a victory."

Parris scored a delegate sweep in his 8th Congressional District portion of Fairfax County that gave him several hundred votes. But Durrette picked up enough votes in Fairfax's 10th Congressional District to foil Parris' plan to use the Fairfax results as evidence of his strength as the delegate selection process continues elsewhere in the state.

Exact figures on the number of Fairfax delegates that went to Durrette and Parris were not immediately available.

Dick Leggitt, Parris' chief political aide, said the question of whether Parris picked up enough votes to stay in the race "is something we are going to have to assess."

Before last night's balloting, Parris, 55, had described the contest as "lights out in Dodge City" if he failed to gain ground on Durrette, who claimed to have 85 percent of the 1,951 votes he needs to win the GOP nomination.

Parris claimed last night to have 1,288 votes in the race in which delegates do not have to declare their allegiance publicly. He said that he is still in the race. "We have absolutely no thought of withdrawing tonight," he said. "It's halftime and the score is tied."

In addition, Parris' aides said the apparent Democratic nomination victory Monday of state Attorney General Gerald L. Baliles gave their own campaign new momentum. They said Durrette, who lost to Baliles in the 1981 campaign for attorney general, has geared his race to an expected battle with Lt. Gov. Richard J. Davis, who is considered more liberal than Baliles.

"We have to consider that in our thinking," Leggitt said. The Parris campaign has sharply criticized Durrette's "electability," saying he lost to Baliles and has not won an election since 1975.

An estimated 2,800 people turned out for last night's delegate selection meetings, some of which erupted into bitter contests between Durrette and Parris forces over parlimentary maneuvers.

Fairfax County also was a strategic battleground in the bids for the lieutenant governor nomination by former state attorney general J. Marshall Coleman of McLean and Richard A. Viguerie, a spokesman for the New Right movement. Party officials said it was unclear last night how the two campaigns fared although large numbers of supporters for each turned out at several of the caucuses.

The unusually large percentage of home town candidates intensified the races for governor and lieutenant governor in Northern Virginia. In addition to the bitter Durrette-Parris fight, four of the five candidates for lieutenant governor have local ties, diluting home district support considered vital to successful campaigns.

The campaign for the second place on the ticket has strained local GOP leaders split over the divergent party ideologies that have echoed the national debate within the party. At one end of the spectrum is Viguerie, who has gained a national reputation as a leader of the GOP New Right. At the other end is Coleman, a party maverick who has been shunned repeatedly by the Richmond party regulars.

The other candidates for lieutenant governor are state Sen. John Chichester of Fredericksburg, Washington lobbyist Maurice Dawkins of Springfield, and state Del. A. R. (Pete) Giesen of Augusta County.