A group of Republican strategists in Fairfax County, fearing that infighting between conservatives and moderates could cost the GOP control of the Board of Supervisors, is forming a political action committee to try to bring the factions together.

Organizers of the PAC, to be called Unity '87, have scheduled a news conference for Thursday to announce that the group will drum up money and volunteers to assist the seven Republican candidates for the board who are facing opposition in the Nov. 3 elections. Six of them faced no opposition from party members in today's primaries.

In particular, the group expects to support Board Chairman John F. Herrity, who is facing Democratic Supervisor Audrey Moore of Annandale in what is expected to be a close race.

Organizers of Unity '87 include a direct-mail and telemarketing specialist and two former Fairfax Republican chairmen, one of whom is a close associate of Herrity's. They say they can raise at least $100,000.

In the process, they hope to put at least a temporary halt to the protracted discord between party conservatives and moderates, increase Republican turnout on Election Day and bolster the countywide network of precinct workers.

"The game has been trying to put together all of the warring factions inside the Republican Party," said Joe Ragan, a leader of Unity '87 and an adviser to Herrity. "The public is not going to elect Republicans unless they see we have our act together."

The formation of the group is another sign that the infusion of dollars into local races in Fairfax this year will go far beyond previous standards for suburban political contests in the Washington area.

Herrity, for example, has already raised more than $100,000.

After a century of Democratic domination, Republicans took control of the nine-member county board in a special election in 1984. But this year, with all but one Republican incumbent facing stiff reelection fights, GOP strategists are worried that the Democrats may be poised to recapture a majority.

One cause for anxiety is that the party has been plagued for several years by a bitter split between conservatives, led by former Air Force Brig. Gen. Benton K. Partin, and moderates, represented by most of the party's elected officials.

The squabbling exploded two years ago when moderates led a coup to oust Partin as chairman and installed former county sheriff James M. Swinson in his place.

Since then, according to many Republicans, the factions have taken turns sniping at each other, to the general detriment of the party.

The executive committee of Unity '87 is composed of six men -- three of whom helped to install Swinson as chairman and at least two of whom sided with Partin.

The organizers said the group will not make direct contributions to candidates but will act as an adjunct campaign -- using the funds to enlist volunteers and to run a phone bank and public relations campaign.

One of the organizers, Michael W. Thompson, heads a group of companies under the umbrella of Thompson Communications that specializes in telemarketing, mailing lists and direct-mail operations for conservative causes.

In addition to Ragan and Thompson, the executive committee of Unity '87 is composed of Dave Foreman, chairman of the county GOP from 1972 to 1975; Ben Cotton, a lawyer active in local politics; John Ryan, a Washington lawyer who is the Dranesville District Republican chairman, and Chad Gore, executive director of the Council for National Defense, a conservative PAC.