LED EVER RESOLUTELY by their tough-talking chairman, John F. Herrity, members of the Fairfax County supervisors have become accessories to a political holdup of all the other jurisdictions in the region. The members are turning into recidivists, too, as Chairman Herrity keeps teasing, threatening and refusing to pay the Metro Transit system.

While Mr. Herrity has never claimed to possess great regional vision, he apparently can't see past the end of his county line these days; in periodic bursts of provincial grandstanding, he and his board either threaten to withold county payments due Metro or actually move to hold the money ransom in attempts to extract various concessions form transit management. Even if this anarchic behavior is merely for local political consumption, it is reckless way to do business with the rest of the region.

At last report, Mr. Herrity & Co. were into what might be called the temporary-relent stage: The board has agreed to pay Metro $621,000 in interest on more than $15 million that the county withheld for 10 months in a protest against Metro's bookkeeping methods. Not only did this with withholding threaten Metro's financial structure, but Fairfax made money on the side by earning $1.1 million in interest on the withheld sum.

That Metro could make inprovements in its financial reporting procedures was not disputed by general manager Richard S. Page -- and he says steps are being taken to carry out recommendations that have accompanied the latest dispute. But already Mr. Herrity is at it again, grumbling that maybe not everything is satisfactory and that "when the next payment comes up, we'll have to see whether they've changed their attitude or not."

Next thing you know, Mr. Herrity and his colleagues could decide they don't like the way Metro's Mr. Page parts his hair and will therefore chip in nothing until he sets it straight. Frugality and tight management are sound objectives for a regional system, and Metro management is not beyond ciriticism by the member jurisdictions. But the financial responsibility for Metro, like its services, must be shared -- not toyed with every other month for purposes of ransom.