The Fairfax County Board of Supervisors said yesterday it would no longer tolerate unanticipated increases in the amount of money that Fairfax must pay to Metro to keep buses rolling in the county.

The board voted unanimously to send a letter to Metro general manager Theodore Lutz, telling him that the county would not pay an additional $2.25 million in Metrobus subsidy for the current year unless Lutz could come up with a "satisfactory explanation" of why the increased subsidy is needed.

"This increase is something I don't think any of us can stand," said longtime Metro supporter Sup. James M. Scott (D-Providence). "We can't afford this kind of misjudgement. Somehow we have to get their attention."

Scott and the rest of the board were angry yesterday about the $2.25 million dollar Metrobus subsidy increase, which jump the county's payment by 31.2 percent to $9,430,000. because the board knew nothing about the increase when it prepared its budget last spring.

Shiva Pant, director of the county's Office of Transportation, said yesterday that Metro does not provide accurate information to the local jurisdictions which support it because "they (Metro) do not track their ridership close enough."

Lutz admitted yesterday that Metro "has a long way to go" in supplying accurate information to local jurisdictions on how much they will have to pay for bus service.

He said subsidy requests are "estimations" that can be wrong. "We prepare these budgets before the impact of such things as fare changes are actually known," Lutz said.

"We are trying to get more ridership information about each bus line on the computer to measure the impact more quickly," Lutz said.