Northern Virginia Rep. Stanford E. Parris and his Democratic opponent, Herbert E. Harris II, spent the last weekend of their bitter campaign mobilizing their supporters for what many expect to be the closest congressional race in the Washington suburbs.

Harris, who is attempting to regain the seat he narrowly lost to Parris two years ago, has been whittling down what GOP polls had showed as a Parris lead. Tuesday's election, the third confrontation between Harris and Parris, has focused almost exclusively on the candidates' longtime enmity, their slashing attacks on each other, and their opposing views on who is to blame for the current recession.

Rep. Frank R. Wolf, Parris' freshman colleague from Northern Virginia, has run a more sedate campaign against former state legislator Ira M. Lechner of Arlington, considered by many to be the underdog. In a final blizzard of targeted mail, Lechner has sought to link Wolf with Reaganomics. Wolf has largely ignored Lechner and stressed his local accomplishments.

Residents of Alexandria, southern Fairfax County and portions of Prince William and Stafford counties live in the 8th District, where Parris, Harris and Citizens Party candidate Austin W. Morrill Jr. are on the ballot. The 10th District, where Wolf, Lechner and Libertarian Scott Bowden are running, includes Arlington, northern Fairfax and Loudoun County.

Northern Virginia voters will also elect 21 state legislators Tuesday from new single-member districts that have forced many incumbents to defend their records against unusually sharp attacks. Winners will serve a special one-year term in the House of Delegates in Richmond.

Democrats in Arlington hope to recapture control of the five-member county board by replacing chairman Stephen H. Detwiler with Mary Margaret Whipple. Democratic candidates throughout the region, including Lechner and Harris, also hope Senate candidate Richard J. Davis will make a strong enough showing in Northern Virginia to give them a slight boost.

Arlington voters will decide a hotly debated referendum on whether to create an independent housing authority, while Fairfax County is asking voters to endorse three bond sales for roads, parks and Metro construction. And in Fairfax City, the recent embezzlement conviction of former treasurer Frances Cox has generated considerable interest and attracted a field of five candidates.

Overall, campaign strategists are predicting that between 50 and 60 percent of the area's registered voters will vote in the off-year elections.

Both Parris and Wolf, two of the 52 Republican congressmen elected in the Reagan landslide, were targeted for special help and money from their national party. Both congressmen loyally supported Reagan's budget in 1981 and then tried to distance themselves from the president this year.

With almost $2 million spent in the two races, the Republicans held a clear edge in money for advertising, mailing and polling. More than a third of the incumbents' dollars came from corporate and conservative political action committees, with Wolf ranking 10th nationwide and Parris 16th in contributions from oil and gas interests, according to calculations by the Citizen/Labor Energy Coalition.

Harris and Lechner collected substantial PAC money of their own, much of it from government employe and other labor unions. More than 40 percent of the households in both districts contain at least one federal worker or retiree, and the Democratic candidates pitched their campaigns toward them.

"They feel threatened, they feel like they've been mistreated, they feel their rights have been jeopardized," Harris said yesterday.

Parris, who was trounced by Harris in the post-Watergate election of 1974, said he does not believe voters, including federal employes, are as angry at him or the administration this year. "There's not that strong feeling of 'Let's send a message,' " Parris said Friday as he knocked on doors in Springfield, a Republican stronghold.

Parris, 53, ran a technologically sophisticated campaign, using pollsters from Michigan and Texas, direct mail consultants from Richmond and Alexandria and a media consultant from suburban Maryland. Harris, 56, relied on the same team of workers that has been with him since his first congressional race in 1974 and said more than half his volunteers were senior citizens.

The race featured unusually harsh broadcast commercials. Parris ads labeled Harris deceptive and "full of hot air," graded him "failed" as a congressman and accused him of wanting to force all federal workers to join unions. Harris responded with ads branding Parris an enemy of Social Security, Medicare and federal employes.

Although the candidates differed on environmental questions, school prayer, and the Equal Rights Amendment, they agreed the economy was the major issue in their race. Parris repeatedly accused Harris of being a "spend-and-spend" liberal masquerading as a moderate, while Harris said Parris was a heartless friend of big business who had betrayed his own conservative principles by voting for record federal deficits.

Wolf and Lechner, by contrast, focused on Wolf's congressional record. Lechner accused Wolf of breaking his campaign promises by voting to cut Social Security benefits and eliminate semi-annual cost-of-living increases for federal retirees.

Wolf, 43, defended his votes as part of an overall Republican budget and said he had worked hard and effectively with Democrats as well as members of his own party. In nearly 40 debates, Wolf ticked off what he claimed as his accomplishments, including his efforts on behalf of the administration's National Airport policy.

Lechner, 48, who has lost two consecutive bids for lieutenant governor, sought to overcome the antipathy of some Democrats who dislike his liberal politics and sometimes brash style. His campaign was troubled by organizational problems and staff turnover. By contrast Wolf enjoys wide popularity within his own party and is expected to benefit from a political organization he has nurtured since 1975 when he first ran for Congress.

Party leaders expected incumbents to triumph in most state legislative races, but said they believed a few to be vulnerable. Democrats are hoping to unseat Robert T. Andrews, who is being challenged by Marie Ridder in a district stretching from McLean to Loudoun County; Frank Medico, being challenged by David L. Temple in Mount Vernon; Kenneth B. Rollins, challenged by Donald W. Patterson Jr. in Loudoun and Fauquier counties; and Gwendalyn F. Cody, challenged by Nora A. Squyres in the Falls Church area of Fairfax.

Republicans, in turn, had their eyes on Floyd C. Bagley, running against J.A. Rollison III in Prince William County; Marian Van Landingham, an Alexandria freshman being challenged by Linda H. Michael; and the seat formerly held by John H. Rust Jr., where Republican primary victor Stephen E. Gordy is facing Democrat James W. Benson.