For Lynne Purvis, a candidate for the Republican nomination for Virginia's 38th House district, 1983 is turning into the year of the campaign sign.

Late one night recently, someone crept into the front yard of Purvis' home near Falls Church and replaced one of her blue-and-white board campaign signs with three bearing the face of her opponent, former delegate Gwendalyn Cody, of Annandale.

Altogether, Purvis says about 900 of her signs have vanished from the Fairfax County district, and some of her supporters have plans for a stakeout to catch the sign-swipers.

"I called her about it, and she said: 'Lynne, don't lose your sense of humor,' " said Purvis, 40, a real estate agent who is making her first bid for public office in Tuesday's primaries.

"Well, I don't think there's anything humorous about losing $700 worth of signs," Purvis said.

"Nobody in my campaign ever touched a sign," Cody responded.

That's all standard fare in one of Northern Virginia's most heated political races, as Cody runs hard to regain a seat she lost last fall.

Cody, a 61-year-old researcher who has been an outspoken opponent of the Equal Rights Amendment, lost narrowly to Nora A. Squyres, a Democrat and ERA advocate, after women's groups targeted her race.

Cody was the only legislative incumbent in the Washington suburbs to lose in the fall elections. This time around, she is focusing her campaign again to challenge Squyres, who won renomination without a primary, on more proven issues. Cody's literature talks about reducing taxes, increasing Northern Virginia's share of state tax revenues, and raising the drinking age.

Purvis has charged that Cody's choice of campaign topics is a deliberate effort to disguise that Cody appears to be "looking for the support of the New Right, the Moral Majority vote. The special interest groups are the ones that can either make or break a primary," Purvis said.

Purvis charged that special interests were behind an endorsement of Cody, mailed yesterday to selected GOP voters who are believed to oppose abortion. The letter bore the signatures of former Republican legislators John S. Buckley and Lawrence D. Pratt of Fairfax, both identified in Northern Virginia with the New Right. In a message printed on the reverse side, the Virginia Society for Human Life urged that voters support Cody because she favors outlawing abortion.

"That's just the good old American tradition of politics--you go to the people who are favorable to your position and try to turn them out to vote ," said Buckley. "There's nothing sinister about that."

Cody, who works part-time for an organization affiliated with the Americans United Against Union Control of Government, says she is trying to run a positive campaign and says that she is not associated with either the New Right or the Moral Majority.

"What does she Purvis know about the new right or the old right?" Cody said. "Nobody ever heard of her until she held that fund-raiser for gubernatorial candidate J. Marshall Coleman a few years ago."

Purvis, a member of the county Republican Committee who volunteered as a part-time aide to Del. Robert Andrews (R-Fairfax) this spring, has peppered her campaign with attacks on her opponent.

"As a freshman delegate, you're supposed to keep your eyes open and your mouth shut and your brain engaged. And from all reports, that wasn't the way she operated," she said.

Like Cody, Purvis is going door-to-door with campaign literature calling for fiscal restraint, a greater local share of state tax revenues, and elected school boards.

Purvis calls herself a fiscal conservative and says the greatest difference between herself and her opponent lies in the realm of social issues. Unlike Cody, Purvis favors the ERA and opposes any move to make abortion illegal. With less than a week to go until the election, both candidates have spent about $6,000 on their campaigns, and both are forecasting a low voter turnout and a narrow victory.