There are five Democrats and an independent running against five Republicans for the Virginia House of Delegates in southern Fairfax County this fall. But it appears the Republicans have still another opponent: each other.

At a recent joint appearance for the candidates, Warren E. Barry, a Republican seeking re-election to his fifth term, was criticized by one of his running mates, John Adams, for favoring collective bargaining rights for public employees.

Barry, who is less conservative than the four other Republicans on the ticket, has been "ostracized" by the four because they say he is too liberal. Lawrence D. Pratt, a member of a three-man conservative team that defeated a three-term incumbent in the Republican primary, has been criticized by supporters of one of his ticket mates for seeking the support of liberal Republicans.

"It's Republican against Republican," said James H. Dillard, the incumbent upset in the June 14 primary. "There certainly isn't any harmony within the Republican ranks."

Normally, Republicans and Democrats alike in Fairfax County run for the House seats on a slate and rarely, if ever, publicly utter a negative word about their running mates.

County Republicans say the "fragmented ticket" is largely the result of the philosophical differences between the "hard-core conservatives," regular conservatives and moderates in the party.

This split is evident in a letter attacking Pratt that was sent out by Alyse O'Neill, a supporter of Robert L. Thoburn, another GOP contender. Thoburn, Pratt and Adams, the conservative team in the primary, were successful in defeating Dillard, whom they had targeted as too liberal to be a Republican.

In her letter to 100 conservative Republicans, O'Neill described many liberal Republicans as being "furious" when Dillard lost in the primary.

"Suddenly (after the primary) things changed," she wrote "Communications between Larry and Bob came to a halt. I immediately called Larry to find out what happened. Larry told me he decided to run on his own as he wanted to "neutralize" the liberal faction.Bob, his family and I were in shock."

"I have been told that Larry now has a new image and prefers not to make an issue of ERA, abortion, and collective bargaining, etc." O'Neill wrote, "He feels our vote is 'in the bag' and therefore he must cater now to "the other side" in order to get elected . . . this behavior is totally unacceptable to me.

Thoburn said he saw the O'Neill letter before it was sent out, but was not involved in writing it. The letter was printed by his son, David, who was paid a fee, Thoburn said.

Pratt conceded that he decided to run a campaign separate from Thoburn.

However, he said O'Neill, who is the chairman of Virginia Stop ERA, a political group seeking to block the state from ratifying Equal Rights Amendment, is mistaken in her criticism of him.

He said there are other issues besides ERA, abortion and collective bargaining. "I told her that after you win a primary the first thing you do is to go out and mend fences," Pratt said. He said he was trying to attract supporters of Dillard.

In response to O'Neill letter, Pratt sent out a letter from Paul M. Weyrich, director of the Committee for the Survival of a Free Congress, a conservative political action group.

In his letter, Weyrich wrote: "Different candidates excite different people . . . The same people who are impressed and will work for Bob Thoburn are not necessarily the same people who will do the job for Larry Pratt and vice versa. There are enough people to go around for Larry and Bob and John Adams and Bob Harris . . ."

Weyrich did not mention Barry who said he was not surprised that he was not included.

"I feel totally ostracized" from the other four GOP candidates, Barry said. He said some Republicans feel the party's candidates should have the same conservative views, but "I don't believe in homogernized Republicanism."

The five Republicans seldom appear at each other's functions. Barry's four ticket mates did not appear at a fund-raiser of his last Friday. Only two candidates - incumbent Del. Robert E. Harris and Barry - attended a Pratt function on Monday.

"The candidates run their own show," said Thomas Davis, vice chairman of the county Republican committee. "I think the (Republican) Party people would like to see them run together, but we can't control them."