Warrenton lawyer Guy O. Farley Jr. launched his candidacy for the Virginia Republican Party's nomination for lieutenant governor today, a race that could prove a major test of the political strength of the state's Christian Right.

Farley, 48, a former state legislator from Fairfax County with close ties to Moral Majority head Jerry Falwell of Lynchburg, is expected to make a strong run for the nomination in a three-way race against Herbert Bateman and Nathan Miller. Both Bateman and Miller are Republican state senators whose appeal is to the more traditional wing of the GOP.

Many Republican leaders are said to privately fear that Farley's nomination could split the party and lead to victory for the Democrats this fall.

Besides support from conservative fundamentalists, Farley also can count on strong backing from the leaders of Ronald Reagan's state campaign. One of Reagan's earliest and most loyal Virginia supporters, Farley was state chairman of Citizens for Reagan and Bush.

Farley's announcement speech today downplayed his involvement with fundamentalist politics, stressing instead his "commitment to those fundamental values and principles that form the foundation of our state and nation." When asked about his ties to the Moral Majority group, Farley said "there is no connection," but added that he welcomed support from Falwell and anyone else.

A born-again Baptist, Farley served in the General Assembly as a Democrat during the 1960s, but switched his allegiance to the GOP in the early 70s contending the Democratic Party had become too liberal. He disappeared from the political scene for several years, but reemerged last year as a key figure in the Reagan campaign.

At last summer's Republican National Convention, he lad a successful effort to eliminate support for the Equal Rights Amendment from the pary platform and to include a plank endorsing an antiabortion Constitutional amendment.