The Fairfax County Board of Supervisors is, according to its vice chairman, Martha V. Pennino, "a very reasonable, rational," body of legislators.

Asked, however, to explain why eight supervisors, including herself, abstained on a crucial vote Monday night and let the ninth member, Audrey Moore, pass two multimillion-dollar sewer rates all by herself, Pennio said: "We wanted to scare the bejeezus out of her."

To say that Moore and her colleagues are antagonists is to say that water is wet. When she takes the floor and begins her 1,000th attack on growth in the county, eyes roll, teeth grind and fists clench.

For her part Moore announcers, time and again, that she is shocked to discover how easily her colleagues "surrender," "cave in" and "capitulate" to developers.

On the rare occasions when Moore isn't at her seat, the supervisors' Monday sessions can be as electrifying as a meeting of the Fairfax County Tree Commission.

On Monday, Moore very definitely was at her seat. She warmed up by voting against a successful motion endorsing the reopening of negotiations between the county and Fairfax City, an independent jurisdiction in its midst. The city and county have been fighting over the costs of services the county provides the city.

Later, she was the only supervisor to vote against a proposal to rezone 435 acres for new homes in the area that drains into the Occoquan Reservoir. Moore says construction of houses in the Occoquan watershed speeds up pollution of the reservoir, which is the main source of drinking water for 600,000 Northern Virginians. The other supervisors resent her frequent votes against such rezonings. They say she is "grandstanding" against growth, and voting against project the Virginia courts have said the county must allow.

Then, as the clocked ticked toward midnight, the Board took up the question of how much sewer rates should be raised. It appeared that the supervisors would adopt one of County Executive Leonard L. Whorton's options --and none in the hookup charge for new homes Moore was expected to vote no, favoring instead a smaller rate increase but a big one in the hook-up fee.

None of the supervisors was enthusiastic about supporting a steep increase in the service rate -- about $91 annually -- but the county's failure to win federal funds for a big sewage project ordained such an increase, Whorton had argued. The project, called the pumpdown, involves pumping sewage from the north of the county to a treatment plant in the south.

What was especially galling to the supervisors was that Moore had, alone on the Board, fought federal funding for the pumpdown. As a result, they said, they were being asked to approve a big increase in the service rate -- while their adversary, the person they considered responsible for their dilemma was supporting a smaller one. Whether it was the lateness of the hour, the fact that the supervisors had worked straight through dinner or the fact that the temperature in the board room had fallen below 65 degrees, the meeting began to take a bizarre turn.

After Moore proposed a 24 per cent increase in the sewer service rate and a 125 per cent increase in the hookup charge, Pennino proposed that the supervisors let Moore set the sewer rates as she saw fit. They could do that by abstaining on the vote on Moore's motion.

The supervisors did, and Moore's motion passed 1 to 0, with eight abstentions.

Explaining her actions yesterday, Pennino said: "She (Moore) was game playing, she was grandstanding. She assumed we'd pass a higher rate."

Supervisor James M. Scott (D-Providence), who had gotten up from his chair and urged individual Board members to abstain, offered this explanation:

The Board members were fed up with the way Audrey has handled this whole matter -- particularly her efforts to undermine federal financing of the pumpdown. . . Finally we said we had enough. I think it showed how little credibility she had with other members on the Board."

Moore dates her estrangement from other members of the Board to 1972. "I know they (the other supervisors) didn't want to control growth even though they sounded as if they did. After 1972, it was fasten your seat belt, here we go."

When Moore, of Annandale, is in the minority on growth issues -- which is most of the time -- she will sometimes accuse the other supervisors of accommodating developers. In a county where growth has been a bitterly fought issue for 18 years, such charges are not accepted as part of the normal political give-and-take.

"It doesn't have anything to do with political philosophy," Scott said. Moore, like a majority of the board, is a Democrat. "It's the way she approaches the staff and her colleagues that causes her most difficulty. She has questioned their integrity."

Moore defends her sometimes go-it-alone approach, "I'm not there to represent the other supervisors and their constituencies, whatever they might be."

As for her successful effort to get the Environmental Protection Agency to reject the Board's attempt to get funding for the pumpdown, she says: "They (the supervisors) knew it was illegal. Not only was it illegal, it was not morally right." The other supervisors deny this.

"I have certain ethics and standards. And I wasn't elected to run a popularity contest," she said.