Virginia State Del. Martin H. Perper (R-Fairfax), who lost his bid for reelection in the Republican primary this fall, has filed a $1.5 million libel suit against Republicans for Conservative Government, charging that the group mailed a misleading letter to voters that cost him his seat in the Virginia House.

The suit -- which also names as defendants Joseph Ragan, chairman of the conservative group, and Daniel J. Arico, the group's treasurer -- was filed last week in Fairfax County Circuit Court. The suit claims that the conservative group injured Perper's reputation by allegedly mailing a two-page letter to voters in the 49th House District before the Sept. 8 primary that misrepresented Perper's stand on abortion and claimed his candidacy was supported by homosexuals. The suit also claims the defendants conspired to injure Perper's reputation.

Perper's lawyer, David L. Duff, said the case could decide what limits, if any, should be placed on the wording of direct-mail appeals. Direct mail has been widely used by conservative groups in recent Northern Virginia campaigns, inspired by the successes of direct-mail wizard Richard Viguerie of Falls Church. Viguerie, who has aligned himself with most conservative elements of the national Republican Party, operated a direct-mail campaign in the general election two years ago that was seen as instrumental in helping Del. John S. Buckley (R-Fairfax) win a seat from the 51st House of Delegates District in Fairfax.

"This is the first I've heard of it," said Daniel J. Arico, when asked about the suit. "I don't want to comment until I've talked to my lawyer." Ragan could not be reached for comment.

Perper, a 42-year-old management consultant who had served in the Virginia House since 1978, lost last month's Republican primary by 100 votes during a bitter campaign. Perper has contended that last-minute direct-mail appeals figured heavily in his defeat. The district, which includes some of the wealthiest neighborhoods in Fairfax County, encompasses Great Falls, McLean and Falls Church.

Perper was one of six Republicans seeking nomination for three House seats from the 49th District. The campaign was marked by extensive direct-mail campaigns by supporters and opponents of conservative candidates attacking candidates for their support or opposition to a number of issues, ranging from religion to the Equal Rights Amendment.

"There's been a rise in the use of direct mail in politics," said Larry Sabato, a University of Virginia government professor regarded as an expert on Virginia politics. "But it's so extremely difficult for a candidate to prove libel," Sabato added, since candidates are public figures and have to prove malice.

"But whether or not you can prove it in court, direct mail is fairly vicious," Sabato said. "It's designed to be emotional and very negative in tone."

The letter that is the subject of Perper's complaint urged Fairfax residents to vote against Perper and vote for three GOP candidates supported by Republicans for Conservative Government: Thomas Cagley, 41; Gwendalyn F. Cody, 58; and Claiborne (Buck) Morton, 51. Only one of those candidates, Cody, won a primary nomination.

The letter, which was allegedly signed by Ragan and mailed Sept. 3, asked voters: "Do you think that a Republican who is supported by homosexuals and radical feminists should represent McLean and Falls Church in the legislature?"

The letter claimed that Perper had voted for higher taxes and government-funded abortions and was endorsed by a Washington homosexual group.