Fairfax County officials, saying they are "fed up with the overall reluctance" of Falls Church officials to cooperate on several interjurisdictional issues, are threatening to sue the city for $271,000 in unpaid construction costs on the jail and courthouse they share.

County Executive J. Hamilton Lambert said it is "highly probable" that the suit will be filed. The county Board of Supervisors is expected to consider at its July 25 meeting whether to file the suit.

Falls Church City Council member W. John Cameron said he regrets the county's move. "We had not by any means exhausted all the possible remedies. I think a suit is just an unnecessary expense."

The disagreement revolves around how the money must be paid. Falls Church wants to repay it in installments, which it has been doing on an annual basis. Fairfax wants the money in a lump sum.

The county and city have been involved in "friendly negotiations" over the payments for several years, said John F. Herrity, chairman of the Fairfax board. But the city's opposition last week to the county's plan for a gasoline tax disbursement formula was, he said, "the last straw."

"Interjurisdictional cooperation is supposed to be a two-way street," Herrity said. "In this case, it's a one-way street into a dead end."

Carol DeLong, mayor of Falls Church, cast the swing vote on the Northern Virginia Transportation Commission in favor of a compromise formula rather than either of the plans proposed by Fairfax or Arlington counties. Under the compromise plan, Fairfax receives $350,000 less and Falls Church receives $2,200 less than under the Fairfax proposal.

Despite a loss of revenue for Falls Church, DeLong said she believes adoption of the compromise plan "was a more equitable thing to do from a regional point of view." The Fairfax plan, she said, "would have damaged Arlington quite badly."

"To me, the county's lawsuit is blackmail," said Gary D. Knight, Falls Church council member. "But that's not going to bother us."

James M. Scott, a Fairfax supervisor whose Providence district borders Falls Church, said the relationship between the jurisdictions has deteriorated to "an all-time low. I don't recall any time in the past when we've had so many differences."

For several years Fairfax and Falls Church have been at odds over water and sewer service that about 100,000 Fairfax County residents receive from Falls Church.

Nancy K. Falck, the Fairfax supervisor representing the Dranesville district that abuts Falls Church on the north, said the city "sets its water rates artificially high." She said county residents are contributing inordinately high amounts to the city's general fund and, in effect, subsidizing Falls Church real estate taxes.

DeYoung denies this. "We provide the service and set the rates according to what we feel is appropriate considering the cost of operation and the cost of construction," she said.