The Capitol Hill meeting yesterday was billed by its host, Rep. Herbert E. Harris II (D-Va.), as an opportunity for the warring parties to sit down and reason together.

The subject - checkbook-busting sewer rates in suburban Prince William County - has triggered heated debate among Northern Virginia officials and created a water boycott by some Manassas Park residents.

But Harris, trying to defuse the situation, managed to get all the parties to agree to work toward lower rates, especially in Manassas Park, which has seen rates climb as much as 400 percent since an $82 million regional treatment plant opened in July.

But as the Harris-inspired meeting was concluding with promises of better cooperation, few in the room were aware that Manassas Park Mayor Frank Murphy was sitting two chairs away from the congressman with a bombshell that would undo much of their harmony.

As soon as the meeting ended; Murphy left Capitol Hill and went to the U.S. Court of Claims on Lafayette Square, where he filed a $12 million lawsuit against the federal government over the dispute.

When Harris learned of the suit soon afterward he was dismayed. "I just don't know what to think," he said. "I have very little faith in attempting to have problems like this resolved in court suits . . . The answer usually is in better cooperation rather than confrontation."

Mayor Murphy refused to discuss the suit.

Manassas Park, which has seen its sewer rates more than triple since the regional plant opened, contends that Environmental Protection Agency requirements, which are no longer in effect, were largely responsible for the massive escalation of the plant's construction costs - from $49 million to $82 million.

Whatever the reasons for the escalation, the local contribution (shared by Manassas Park, Manassas, and Prince William and Fairfax counties) rose from $11.9 million to $24 million. The difference is the amount sought in the suit.

Most of the meeting was devoted to what Virginia state Sen. Charles Colgan (D-Prince William) said consisted of "pointing his finger at the other guy." It also was marked by an impassioned plea by the leader of protesting Manassas Park residents whose average annual sewer bill has jumped from about $100 more than $300.

"I can't afford to pay this outrageous (sewer) bill," Buddy Hite, president of Concerned Citizens of the City of Manassas Park, said, looking down the table at Thomas Jorling, deputy administrator of EPA. "If you don't do something about reducing costs (of sewage treatment plant construction throughout the nation), you'll bankrupt only me, you'll bankrupt the country."

Jorling, who took most of the heat at the meeting, replied, "I'd like to have a tape of your remarks . . . What you have said is support for a lot of thick documents we have tried to get into this program, but we've been meeting resistance (on the state and local levels)."

Jorling's comments were aimed, in part, at another dispute, involving Montgomery County's attempt to build a major regional treatment plant that would have cost more than $400 million. EPA, claiming the project was too big and costly, votoed it, and was upheld in a court appeal earlier this year.

Although Manassas Park is suing - and inviting its neighbors to join in the legal battle - the city and EPA will work on developing a cost-reduction program that would permit the city to lower its sewer rates.

Jorling disputed an analysis by the Upper Occoquen Sewage Authority contending that its costs rose by $33 million because EPA required the regional plant to be built in sections. Jorling said the EPA requirement was responsible for only 10 percent of the increase. However, an EPA memo written by Joseph A. Galda of the agency's regional headquarters in Philadelphia said" the segmented project will require $11 million more in grant funds and three more years to complete."