Republican Thomas M. Davis III, a three-term Fairfax County supervisor, announced his candidacy yesterday for chairman of the Board of Supervisors, calling the county government "a rudderless ship."

"As I've seen how this board works over the last three years, I've been increasingly concerned with the direction this board has taken. I have felt it was time for a change," said Davis, speaking before a crowd of supporters at the Annandale Volunteer Fire Department last night with his wife and three children at his side.

In a brief, low-key speech that did not mention incumbent Democratic board Chairman Audrey Moore by name, he implicitly criticized Moore's leadership and called for a better relationship with the business community, which has been angered by Moore's slow-growth policies. "I've seen us blow it," Davis said.

Davis called for a more responsive county government made up of an elected county executive, an independent auditor reporting directly to the supervisors, staggered elections for supervisors and more autonomy so the county can implement laws without permission from state lawmakers in Richmond.

Unlike Maryland, where county executives are elected and are the political equals of strong mayors, Virginia county executives are appointed by the boards and manage the bureaucracy at the members' pleasure. County governments in Virginia often are frustrated when it comes to implementing most major policies because they first must get permission from the state.

Davis, 42, is expected to conduct a campaign that appeals to voter frustration over rising property taxes and continued traffic congestion. To that end, Davis's call for an elected county executive is intended to attract residents who saw former county executive J. Hamilton Lambert as a symbol of rising taxes and expensive county services.

Davis comes from the Mason district, an older, more urban area of the county where he has built a strong base through attention to constituent desires and an uncanny ability to keep both sides happy during disputes.

"I'm a consensus builder," the Virginia native said.

Davis's boyish earnestness, approachability and talent for witty quips have served him well, often propelling him into news stories that carry his name outside the confines of his district and into various corners of the 399-square-mile county.

But that affability, what many call an eagerness to be liked, also may be his biggest political vulnerability. Many Fairfax residents, politicians and members of the business community complain that Davis often straddles the fence and they do not know what he stands for.

"That's hogwash," Davis said. "I've cast 8,000 votes on the board. There's nothing wishy-washy about that."

In the past four years, Davis has championed affordable housing and successfully sponsored an ordinance providing for no-smoking sections in restaurants.

But he has voted for many of the budgets that now are causing taxpayers to grumble. And although he voted for Moore's proposal to reduce development on thousands of acres of commercial and industrial land, he voted against a measure to appeal a judge's ruling that nullified the legislation.

In what could become a political issue, Davis said he would accept contributions from developers, but he added that "developers aren't going to be substantial players" in his campaign. Moore is expected to repeat her pledge not to accept campaign contributions from developers.

Although the chairman has no more power than the other board members, all of whom serve four-year terms, the high-profile post carries extraordinary prestige. The chairman, whose salary is $45,000, generally is considered the county's leading spokesman and, as such, plays a major role in dealing with the state government, forming public opinion and setting the county's agenda.

Davis is a lawyer and corporate officer with the McLean-based Planning Research Corp. He grew up in Northern Virginia, graduated cum laude from Amherst College and attended the University of Virginia law school, from which he received a degree in 1975.

He was elected to the Board of Supervisors on his first try in 1979, and in his first two terms he developed a close working relationship with Moore, with whom he shared a border when she was the Annandale district supervisor. That relationship deteriorated after Moore was elected board chairman in 1987.

Although Davis has about $100,000 in his campaign war chest, he is facing an aggressive challenge by former chairman John F. "Jack" Herrity. The Republican nomination will be decided at an August convention, a structure engineered by Herrity to appeal to his community strength and organizational skill.

Davis hopes to garner an overwhelming majority on May 18, when those who wish to be delegates must register with county party officials, turning the August convention into a formality and enabling him to concentrate on his campaign against Moore.

Herrity is expected to formally announce his candidacy in two weeks.