Northern Virginia Rep. Stanford E. Parris, whose aides recently disparaged negative advertising as the mark of a loser, has begun a $100,000 final television assault, repeatedly grading his opponent "failed" in scarlet letters flashed across a black screen.

Parris' opponent, former Democratic Rep. Herbert E. Harris II, has begun his own final media attack, using Parris' voice to link him to a budget resolution that would have cut education and Social Security benefits. "I voted for it, and I make no apologies . . . . I would do it again," Parris intones repeatedly as an announcer recounts the proposed cuts.

"On Nov. 2, it's your turn to vote," the ad concludes. "Herb Harris. A friend we can count on."

The Parris campaign, fearful that negative advertising might backfire, had planned to ignore Harris' attacks and focus on the incumbent's accomplishments. Those plans changed as polls showed Harris, who was unseated by Parris in 1980, gaining ground in a very close race.

"We don't call them negative," a Parris aide said. "We call them self-defense."

Self-defense or not, the Parris ads carry a punch. "Don't be fooled by the Herb Harris distortions," says one TV spot.

The strident commercials aired by Harris and Parris contrast sharply with those in Northern Virginia's 10th district. Parris' fellow Republican Rep. Frank R. Wolf is spending only $18,000 on his final advertising campaign against Democrat Ira M. Lechner, who was reported trailing Wolf and is running no television ads.

The contrast in the region's two districts reflects more than the closeness of the Harris-Parris race and the enmity they have developed during a decade of opposing each other.

"Stan's strategy is to polarize his people and get them to support him, while Frank's is to try and make it comfortable for conservative and moderate Democrats to live with him," Wolf consultant Ed DeBolt assessed the two incumbents.

None of the candidates is relying entirely on broadcast advertising in the final stretch. Parris has mailed 200,000 letters this week, with 50 different messages targeted to special interest groups. Lechner began a $7,500 radio campaign yesterday and will have mailed more than 750,000 letters.

Nevertheless, the television ads have grabbed the largest share of campaign funds and public attention. Last month Parris sent Harris on a mythical radio voyage in a "hot air balloon." Those commercials impugned Harris' integrity and ridiculed his purported support of funding junkets to the Caribbean and studies of the mating habits of ducks and the speech patterns of Philadelphians.

After a poll showed both candidates losing ground because of apparent voter disgust over the mud-slinging, Parris temporarily dropped his negative ads.

Parris, who has attacked Harris as an untrustworthy liberal who voted for "every crackpot socialistic scheme," also has sought to appear disdainful of Harris' combative style. "We wanted to create some impression that he's not screaming back as much as Herb is screaming at him," said Parris campaign manager Fred Allen.

In some of the 97 television spots he has booked for the final week, Parris recites some of his accomplishments, alternating with claims that Harris "tried and failed" to do the same. Harris, with 37 spots for the final stretch, is running "The Empty Chair," an ad accusing Parris of ducking debates before federal retiree groups.

Wolf's television commercials show him posing with his staff on the Capitol steps, walking through Turkey Run Farm, romping with his children and standing outside Dulles and National airports. "He's done a good job and he's kept his promises," say the commercials, echoing the theme Wolf has stressed throughout his campaign.

"Everything -- I mean everything -- is positive," said DeBolt, who estimated Wolf will spend about half of his total $118,000 media budget on more than a half dozen television spots. Wolf also has taken advantage of a new technological bargain, spending $500 for 25 different spots in Arlington's cable system.

Wolf's commercials are an attempt to portray him as a hard-working, effective -- if unexciting -- congressman with broad bipartisan appeal. "Frank is the staple: He's not the gourmet rice and exotic wine," DeBolt said.

Lechner's radio commercials tout him as "the positive Democratic alternative" and hammer away at Wolf's "broken promises" and his votes on federal employe issues and Social Security.

"The commercials are negative in the sense that they talk about Frank's record," said Lechner campaign manager Donald S. Beyer Jr., who said that a challenger has to follow a different strategy from an incumbent. "We can't win by portraying Ira as a smart guy with a wife and two kids who's worked hard."