An article yesterday failed to note that Democrats in Northern Virginia's 38th House district, in eastern Fairfax County, will be choosing a candidate in a primary Sept. 7. Nora Squyres and Wayne Lynch are competing for the right to challenge Republican incumbent Gwen Cody in the Nov. 2 election.

Three moderate Republican state delegates in Fairfax County will face opposition from more conservative opponents in a primary on Sept. 7, intensifying a long-running competition between the party's two wings in Northern Virginia.

The incumbent delegates--John H. Rust Jr., Robert E. Harris and James H. Dillard II are challenged, respectively, by Stephen Gordy, a retired Army colonel and Loudoun County school principal, Robert L. Thoburn, a former legislator and owner of the Fairfax Christian School, and Gordon S. Jones, who said he is a Capitol Hill lobbyist for pro-family organizations.

The incumbents have been targeted by the party's conservative wing before and have generally come out ahead. In this fall's special election, however, Northern Virginia's 21 legislators will run for the first time from single-member districts rather than at large, injecting a new element of uncertainty into the contests.

"I think they'll be very close," Del. Vincent F. Callahan Jr., the House minority leader in Richmond, said of the three contested primaries, noting that each contest may attract fewer than 3,000 voters.

Democratic and Republican candidates for Northern Virginia's 21 House seats met a 5 p.m. filing deadline yesterday, preparing for the unprecedented even-year election made necessary by the state's protracted redistricting battles. The Democrat-controlled General Assembly, required by law to redraw its districts after the 1980 census revealed population shifts, tried several times to draw traditional multi-member districts that would help as many incumbents as possible. The Justice Department, the Republican then-governor or the courts rejected those plans, eventually forcing the legislators to draw a new plan and to stand for election in three successive years, 1981, 1982 and 1983.

The smaller, single-member districts will allow candidates to meet more of their voters while spending less money, several delegates said . They will also allow challengers to focus attention more directly on incumbents' records, they said.

Callahan said he believes the single-member districts will help the GOP, which last year increased its representation in the lower house from 25 to 33. In Northern Virginia, however, where Democrats hold a 12-to-9 edge, leaders of both parties predicted that most incumbents will do well.

Fairfax Democratic Del. Kenneth Plum and two incumbent Arlington Democrats, James F. Almand and Warren Stambaugh, drew no challengers at all, according to officials of both parties. Arlington's third delegate, veteran Democrat Mary Marshall, will face Republican David M. Mason, a 24-year-old legislative aide to U.S. Rep. Thomas Bliley of Richmond, in November.

"We hoped to have three candidates, but they the Democratic legislators carved out three very nice, safe Democratic districts," said Jade West, the Arlington Republican chairman.

Republicans also have hopes of defeating Alexandria Del. Marian Van Landingham, who unseated a Republican last year and will face Old Town architect Linda Michael this fall, Callahan said. Also thought to be vulnerable, he said, is Del. Floyd C. Bagley in Prince William County, who is being challenged by John Rollison.

The Democrats in turn said they hope to unseat Republican Frank Medico, who will defend a district in the Mount Vernon area against David L. Temple, who narrowly lost a bid last year to become the first black delegate from Fairfax in memory.

Schick said she believes two other first-term Republicans also are vulnerable, Robert T. Andrews in a Great Falls-Herndon district and Gwen Cody in Falls Church.