Fairfax County legislator James H. Dillard II should be in good shape this year. Running from a new House district carved out just for him, the moderate Republican has no Democratic opponent and has raised more money than most of his colleagues so far.

Dillard says he is running scared, however, fighting off a primary challenge from the same conservative forces that knocked him out of the General Assembly in 1977.

"There's been nothing like this before," said Dillard, who regained his legislative seat in 1979 and has served a total of nine years in the General Assembly. This summer Dillard, a 49-year-old Fairfax school administrator, has found himself on the defensive, refuting campaign tactics that he calls "a concerted effort at distortion."

Fairfax County's Republican primaries, a perennial source of excitement in recent years, once again are ending in a last-minute flurry of accusatory mailings and charges of misrepresentation. Northern Virginia voters Tuesday will cast ballots in a total of five Republican and two Democratic contests, with the most dramatic pitting conservative challengers against three moderate incumbent Republicans.

The GOP incumbents say the campaigns are more intense this year because they are fighting head-to-head in new single-member districts -- and there is no accurate way of predicting how many voters will turn out for the primaries or whom they will support. The conservative challengers, denying charges of distortion, say the incumbents are worried because the new districts are forcing the legislators to defend their voting records in Richmond.

"It's much less confusing for the voters," said Gordon Jones, a 40-year-old Washington lobbyist who is challenging Dillard as too liberal for his Burke-area district. "Now they have a single delegate to whom they can look for representation. . . and my reading of Mr. Dillard's voting record is that he doesn't represent the citizens of Fairfax County, let alone the Republicans of Fairfax County."

Jones has attacked Dillard for supporting a law allowing housing authorities to finance middle-income as well as low-income housing.

Jones claims the measure amounts to "a substantial expansion of power" for the county's unpopular Redevelopment and Housing Authority.

Dillard says the law will allow the authority to support mixed housing, instead of concentrating poor people in ghetto-like projects. He has responded with a mailing of his own that hits Jones for miscasting him as an advocate of low-income housing.

"My opposition from the far right evidently knows no bounds of decent behavior," Dillard wrote. "I have never supported low-cost housing in Burke or any other area."

Jones, whose Washington clients include United Families of America, a group founded by Sen. Jeremiah Denton (R-Ala.) to lobby on "family issues," also was the beneficiary of a letter sent to local churches, urging ministers to support him because his views are "strongly aligned with Christian ethics" and because he has a "Christian background." "The implication is that I do not," fumes Dillard.

Jones said he knew nothing about the letter. "I would never accuse Dillard of not being a Christian," he said.

Del. John H. Rust Jr., a lawyer running from a new district that includes Fairfax City and nine precincts north of it, also has lashed back at campaign literature put out by his opponent, retired Army Col. Stephen E. Gordy. Like Dillard, Rust said candidates in the new districts can no longer afford to let campaign charges go unanswered.

"It puts a very different complexion on the manner in which you run. In a multimember district, the object is to get the voters to know who you are -- it's kind of like a crowd in a bathtub," Rust said. "In a single-member district, you have to look beyond name recognition. If you let a charge stand, it hurts you."

Rust has jumped on Gordy for "misleading" statements, particularly the charge that Rust has "not exhibited loyalty" to the Republican Party.

He also disputed Gordy's attacked on his voting record, denying, for example, that he favors state funding for abortion.

Gordy says he resents Rust's "questioning my integrity" by challenging the truthfulness of Gordy's "Republican Voting Guide." That flyer labeled Rust a liberal. Gordy said Rust voted to allow Medicaid funds to pay for abortions in cases of rape, incest or fetal abnormality, and that every other charge he made was supported.

For all their defensiveness, two of the three moderates have the edge in the race for campaign contributions. Rust had raised more than anyone as of Aug. 27, the last reporting date -- almost $14,000 in loans and contributions for a race that election officials say may attract fewer than 2,000 voters. Only Del. Robert E. Harris lagged behind his challenger, former Del. Robert L. Thoburn.

All three incumbents -- Rust, Dillard and Robert E. Harris -- received $800 contributions from the teachers' Virginia Education Association political action committee. Dillard also received $200 from Mark Saurs, the Richmond lobbyist for savings and loan associations, and from the state optometrists' lobby. Rust got $150 from a political action committee formed by the Alexandria law firm of William G. Thomas, a Democratic lawyer who lobbies for condominium owners and who worked with Rust on a bill restricting Fairfax's ability to control condominium conversions.

Gordy got his largest donation, $2,000, from former Del. John Buckley, a Vienna conservative who was turned out of office last year and has been turning his campaign funds over to Gordy.

Primary day -- coming the day after Labor Day -- is expected to draw a typically low turnout, which can give an edge to well-organized candidates. In Virginia, where there is no registration by party, anyone registered in a district may vote in either party's primary.

Also competing Tuesday will be James W. Benson and Fred J. Ricci, Democrats running in the Fairfax City-area district; Republicans James N. Burroughs and David Sanders, seeking to challenge Democrat Del. Dorothy McDiarmid; Democrats Nora Squyres and Wayne Lynch, who want to run against first-term Republican Del. Gwendalyn Cody; and two Prince William Republicans, Clancy McQuigg and Smith Young, who want to challenge Democratic Del. David Brickley.