Republican Reps. Frank R. Wolf and Stan Parris easily won reelection in Northern Virginia yesterday, and GOP lawyer D. French Slaughter of Culpeper swept to victory in the 7th Congressional District, a portion of which is in the outer Washington suburbs.

In a hotly contested race in Tidewater, 1st District Republican Herbert H. Bateman of Newport News also won reelection.

In addition to an overwhelming GOP victory in the presidential and Senate races statewide, Republicans maintained their 6-to-4 edge over Democrats in Virginia's congressional districts.

In the 8th District, Parris' 54-to-45 percent lead over state Sen. Richard L. Saslaw, his Democratic challenger, appeared decisive enough to propel Parris into Virginia's 1985 gubernatorial race. Parris, who has long expressed interest in the governor's contest, planned to meet today with supporters to map his political future, aides said.

Parris called his victory "better than even my wildest dreams . . . . It's even better than we had dared to hope."

Parris, 55, resoundingly beat Saslaw, 44, in mostly rural Stafford County and won easily in Prince William and Fairfax counties, but he lost to Saslaw in Alexandria.

Saslaw conceded defeat last night, saying the results show that the Democratic Party may be out of step with Northern Virginia's voters and will have to change.

"Our party is going to have to make a greater effort to incorporate the middle class," Saslaw said last night. "What may have been relevant in the '60s is not relevant today. I think there is a perceived notion out there now that the government is limited in what it can do. The hierarchy in our party . . . has gotten that message today." Saslaw suggested that he may run for Congress again in 1986.

Wolf's 61-to-39 percent victory in the 10th District over Democratic challenger John P. Flannery, a former federal prosecutor and political newcomer, was even larger than Parris' margin. Wolf swamped Flannery in Loudoun County, beat him soundly in Fairfax County and won by a slim margin in Arlington County, a traditional Democratic stronghold.

Slaughter, 59, a lawyer, was beating his Democratic opponent, tax lawyer Lewis M. Costello, 51, of Winchester, by 58 percent to 42 percent, in the race to succeed retiring Republican J. Kenneth Robinson in the 7th District, which includes Fauquier County and parts of Prince William and Stafford counties.

Costello attacked Slaughter for his General Assembly record in the 1960s, when he supported segregated schools and opposed civil rights measures, but Slaughter refused to apologize for past deeds.

In the 8th District -- which includes Alexandria plus southern Fairfax, eastern Prince William and northern Stafford counties -- Parris raised more money than any other House candidate in the Washington area, $794,490. Saslaw, who raised $226,101, repeatedly said last night that Parris' superior finances played a role in that race.

Independent candidate Donald W. Carpenter of Alexandria gathered a tiny portion of the vote in that election.

In the 10th District -- which includes Arlington County, northern Fairfax and Loudoun counties plus the cities of Fairfax and Falls Church -- Wolf outspent Flannery $518,621 to $207,723.

Wolf, 45, said that Republicans' ability to attract new voters, such as young people and recent immigrants, played a role in his victory. Flannery, 38, said his loss was more a result of President Reagan's strength than of his weakness in the eyes of voters.

"We got caught in a strong wind that blew across the Potomac," Flannery said. "I don't think Frank Wolf was a factor as much as the presidential race was a factor."

Flannery and Saslaw accused their incumbent opponents of being too conservative for Northern Virginia.

In Tidewater's 1st District, Bateman easily beat Democrat John McGlennon, a government professor at the College of William and Mary, who ran a hard-charging race, by a 59-to-40 percent margin.

In the state's closest congressional race, freshman Democrat James R. Olin beat GOP challenger Ray L. Garland, a former state legislator, 52 percent to 48 percent in the 6th District, a conservative area that includes Roanoke and Lynchburg.

In the 9th District, including the economically depressed coal region of Southwestern Virginia, freshman Democratic Rep. Frederick C. Boucher beat Republican challenger C. Jefferson Stafford, a state delegate.