For most of this decade, John F. Herrity has been Northern Virginia's leading politician of bluster and media hype.

But with a substantial victory in Tuesday's election returning him to a second four-year term as chairman of the Fairfax County board of supervisors, the 47-year-old Herrity says he is ready to settle down and become a leader.

Even some of his old political enemies agree that Herrity -- who's been blasted as a "demagogue" and worse in acrimonious board sessions -- has a chance now to take command of the region's increasingly conservative suburban electorate.

"Herrity is in an outstanding position to become a major leader in the Washington metroplitan area," said retiring Democratic Supervisor Alan H. Magazine, one of Herrity's consistent critics.

In an interview yesterday, Herrity said he wants to become a consensus builder on the nine-member Fairfax board. He said he wants to be "less visible" and "more dominant."

To command a mojority in Fairfax now -- where Tuesday's election gave Republicans four supervisor seats, a gain of one -- Herrity has only to pick up the vote of one Democratic supervisor. An easy trick, his critics say, if Herrity can resist his tendency to "grandstand" in front of the media.

Tuesday's election also boosted Republican influence in neighboring Arlington County, enabling the GOP to hang on to majority control of the five-member board and propelling Republican-backed board chairman Walter L. Frankland into a similar regional leadership position.

With the re-election of Frankland and his colleagues Dorothy Grotos to three-year terms, Arlington Republicans consolidated a majority position established only last year when Republican Steven Detweiler was elected. Before then, Democrats had been in control for nearly a quarter century.

Republican power also was felt in House of Delegates races in Fairfax where only two of the 10 winning candidates were Democrats.

"It was the worst drubbing the Democrats have taken that I can remember," said Magazine, who chose not to run for re-election. "This will serve notice to the Democrats that we will have to stop taking things for granted."

Politicians from both parties said yesterday the election serves notice that Northern Virginians are gradually becoming more conservative -- more concerned with maintaining the quality of suburban life than with financing social programs.

"There are just an awful lot of people in Arlington who are worried about high taxes in an inflationary economy," said former Republican state Del. Henry C. Lampe. "Grotos and Frankland (in Arlington) were recognized as having brought about the first significant tax cut in years."

In Fairfax, Supervisor Joseph Alexander, a conservative Democrat in Lee District who easily won re-election, said voters want traffic congestion solved and taxes low. They express far less interest in environmental controls, Alexander said, than they did at the beginning of the decade.

Throughout Northern Virginia, one of the major issues facing local politicians is how to pay for Metro without raising already high property taxes.

In Fairfax, for example, the cost of the Metro rail and bus subsidy (now $16.3 million a year) will probably exceed the cost of police or fire protection in the next five years.

Under his leadership, Herrity says the supervisors will be "cautious and conservative" in finding a solution to Metro funding problems. Herrity has expressed his opposition to any plan for a sales tax increase to fund Metro that does not return all taxes raised in Fairfax to the county.

The board chairman, however, was careful yesterday not to preempt or speak for his new Republican colleagues on the board. In the past four years, Herrity's leadership crumbled because he took what many saw as a "lone ranger" approach to soothing the fears of suburbia.

"If he goes it alone again this term, the vote on most of his pet issues will be eight to one," said Magazine. "We are all politicians and if there is anything a politician resents is another politician trying to upstage him.

Thomas M. Davis III, the Republican who replaces Magazine as supervisor in Mason District, and Nancy K. Falck, the Republican winner in Dranesville, are new to the county board and are seen by many observers as more willing to work with Herrity than were their successors.

Davis, who soundly defeated Democrat Betsy W. Hinkle, said yesterday that he will work closely with the chairman. But Davis added that he cannot be counted on to follow Herrity on every vote.

Falck, who trounced Democrat Maya Huber in the McLean-Great Falls area, is a member of the county school board who echoes many of Herrity's ideas on fiscal responsibility.

Herrity, an insurance salesman and graduate of Georgetown Law School, said he will try to help ease the tax burden for homeowners in the county by stepping up the county's already aggressive policy of attracting light industry to Fairfax.

Herrity said Fairfax will need the new industry to offset what he predicted will be a 20 to 30 percent decline next year in new housing starts a decline Herrity said will be caused by higher interest rates.