The Arlington County Board's lone Republican, Michael Brunner, sits on the far right side of the dais but, to the consternation of some of his party's more conservative members, his votes are often down the middle.

Unlike last year, when the five-member County Board had two Republicans, or the year before when it had three, the board's semimonthly meetings have lost most -- but not all -- of their partisan bite.

As a Reagan administration appointee to a top-level Department of Agriculture position, Brunner, 41, has conservative credentials. He also has a moderate bent and personal style that have enabled him to work with the board's four moderate-to-liberal Democrats.

"The board is definitely less cantankerous . . . less raucous, less vehemently split," said a county staff member, voicing a sentiment shared by many others. "They can be partisan without getting personal."

A case in point was the day last year the board, split 3 to 2 in favor of Democrats, adopted a $226 million budget. Before the big vote, which also broke along party lines, the five members squabbled for almost three hours over a $5,000 appropriation to a tenants organization the Republicans considered too friendly to the Democrats.

The other partisan battles that day took far less time, including the one on a $250,000 special fund the Democrats created to benefit teachers, one of their most loyal constituencies. The Republicans yelled "political payoff" and argued that the board should not be giving the School Board money for the fund that it had not requested.

When the budget was adopted this year, the tenants appropriation and the special school fund sailed through the proceedings without objection from Brunner, a former School Board member.

He stood his ground, hewing to the traditional ideological differences between the parties, when it came time to cut the property tax rate. He wanted five cents lopped off the rate, while the Democrats would go for only two cents. So Brunner voted against the budget on principle.

He also has been the lone dissenter on other key votes: against a federal legislative package that endorsed a nuclear freeze and the Equal Rights Amendment, and against the county's new equal employment opportunity policy because he maintained -- to the Democrats' denials -- that it endorsed quotas.

There have been other differences between Brunner and the Democrats that have not gotten very far for reasons of arithmetic. "There's little he can do as one. It's almost impossible because he can't get a second," said Walter L. Frankland Jr., the former Republican board member who was defeated in 1983.

Still, Robert E. Harrington, an unsuccessful GOP board candidate and president of the conservative Arlington County Taxpayers Assocation, says he is "disappointed" that Brunner has not waged more of a battle against the Democrats.

"I suppose you could say he is 'the fifth Democrat,' " Harrington said. He complains that Brunner should have mounted an all-out attack on the tax rate.

Helen Blackwell, chairman of the Arlington Republican Committee, says Brunner "is doing as well as could be expected under the circumstances."

Kenneth Ingram, a moderate Republican and Brunner supporter who is often mentioned as a possible board candidate, gives him kudos. "I can't characterize most of his votes as being pro- or anti-Republican, but more on a case-by-case basis," Ingram said. "He's a good listener, pays attention to citizen input, and makes a strong effort to get out into the community for meetings."

"On the big questions," Ingram added, "he has voted the minority position and articulated the minority position. It's just that his style is not combative or confrontational . . . . He tries, to the extent he can, to reach a consensus with the majority."

County Board Chairman Ellen M. Bozman, a Democrat, agrees that Brunner's "style is different" from some of his GOP predecessors: "He joins in the discussion and uses a softer approach in stating his position. He states it, but in a nonconfrontational way."

As any County Board member can attest, most votes have little partisan basis. Brunner, who is taking a new job in January as the chief executive officer of a telephone trade association, said he has formed most of his positions from his "Second Sunday Group," informal get-togethers with citizens of varying political stripes each month.

"I've never had a problem disagreeing, and I think I do so firmly and forcefully," Brunner said of the "fifth Democrat" charge. "I believe in disagreeing without being disagreeable, and not arguing for the sake of arguing."