Northern Virginia Rep. Frank R. Wolf was reelected last night with a comfortable margin, while his Republican colleague Rep. Stanford E. Parris appeared barely to have hung on to the seat he won two years ago.

Parris claimed victory at 10:30 p.m., saying he had bested former Rep. Herbert E. Harris II in their third and most bitter contest by about 1 percent of the votes cast. But a disappointed Harris, who was trying to regain the seat he lost by an even smaller margin in the 1980 Reagan landslide, declined to concede and said he would await the results of an official vote count today.

Wolf defeated former state legislator Ira M. Lechner with 53 percent of the vote, running well in Fairfax and Loudoun counties and preventing Lechner from overwhelming him in the Democrat's home base of Arlington. Lechner and Harris both appeared to run substantially behind Democratic U.S. Senate candidate Richard J. Davis in most precincts, and some voters who cast ballots in the Senate race declined to vote for either candidate in the Harris-Parris campaign, which had been characterized by negative advertising and personal clashes between the candidates.

"We ran a positive campaign, we talked about the issues and the record and we never attacked anybody," said Wolf, who appeared exhausted as he addressed 300 cheering supporters gathered at the Tysons Westpark Hotel.

"I think what's clear is that people have not yet decided Reaganomics is bad for their health," said Lechner, who also attributed his defeat to the "low pulling power" of Democratic Gov. Charles S. Robb, who appeared at one of his fund-raisers.

Parris told a cheering crowd at the Springfield Hilton that he had defeated his longtime rival "with the usual landslide victory" margin of about 1,500 votes. Unofficial returns gave Parris 69,445 votes, or 49.7 percent, and Harris 67,980, or 48.6 percent. Citizens Party candidate Austin W. Morrill Jr., who many politicians had predicted would siphon votes from Harris, polled 2,335 votes -- more than Parris' margin of victory.

Harris looked pale and tired as he left his campaign's would-be celebration at the Franconia firehouse, acknowledging that he was "surprised at the closeness of the vote and disappointed." But Harris, who failed to run up the comfortable margin of victory in Alexandria that he needed to overcome Parris' lead in Fairfax and Prince William counties, said the race remained too close to call.

"We certainly do not intend to claim victory or make a concession speech until we've seen all the numbers," he said.

While both Democratic challengers appeared unsuccessful in their bids to exploit discontent among federal employes with Reagan and his loyalists, the party made inroads in the GOP's current 9-to-1 hold on the state's congressional delegation. Industrialist Norman Sisisky handily defeated veteran GOP Rep. Robert Daniel in the Southside 4th District, Democrat James Olin won a narrow victory in the open 6th District, and state legislator Frederick Boucher was leading incumbent GOP Rep. William Wampler by 350 votes with 99 percent of the vote counted.

Wolf and Parris won narrow victories in the 1980 Reagan landslide, and this year the national Republican Party gave substantial support to both in their quests for second terms. Their Democratic challengers attempted to link the incumbents to Reagan, in an effort to appeal to disgruntled federal workers and retirees who comprise more than 40 percent of the voters in their districts.

The vitriolic 8th District contest was the third and possibly final battle between Harris, 56, and Parris, 53, familiar figures in Northern Virginia politics for the past two decades, both of whom had knocked the other out of Congress once. Many politicians predicted that the Democrats would not give Harris another chance to run.

The 10th District featured a clear ideological choice between Wolf, 43, a lawyer and former lobbyist who received substantial contributions from corporate and conservative political action committees, and Lechner, a 48-year-old union lawyer who was backed by organized labor and liberal organizations whose causes he long has championed.

Harris also was outspent 2-to-1 by Parris, who apparently was headed toward breaking a Virginia congressional record by raising nearly $700,000. Parris, like Wolf, received more than a third of his funds from corporate and conservative political action committees, while Harris and Lechner received almost half of their money from union PACs.

Harris, who defeated Parris in the Watergate election of 1974 and served three terms in the House, discounted their personal rivalry and attempted to focus attention on Parris' support of the 1981 Reagan budget. Parris, from the day he renounced a U.S. Senate bid because, he said, he wanted to keep Harris out of Congress, portrayed the election as a referendum on Harris and the "crackpot socialistic schemes" that he charged Harris had supported in the House.

Both Wolf and Parris had sought to distance themselves from Reagan this year, although they received help from top administration officials who ranged from Vice President George Bush to Transportation Secretary Drew Lewis. Wolf raised nearly $500,000, compared to $350,000 for Lechner, the vice chairman of the state Democratic Party.

Wolf frequently castigated "the Ted Kennedys and Tip O'Neills, who support my opponent." Lechner, in turn, accused Wolf of being a "Reagan clone" who had broken his promises by supporting cuts in Social Security and retirement benefits for government workers. Toward the end of the race, however, Lechner strategists privately conceded their fears that federal workers were not angry enough to oust Wolf.

In nearly 40 debates, Wolf denied that he had broken his campaign promises and defended his votes as part of an overall Republican budget.