The D.C. government and the state of Maryland have reached an agreement that allows two summer camps in St. Mary's County operated for children from the District to hook up to an underused sewer treatment plant, thus ending a 10-year stalemate.

A $498,000 federal grant awarded Sept. 28 by the U.S. Environmental Protection Agency will pay for 75 percent of the cost of constructing sewer lines from the camps to the 10-year-old plant. The two tax-exempt camps will pay 25 percent of the cost as well as part of the plant's operating and maintenance costs, Maryland state officials said.

Under Maryland regulations, only state-owned facilities are allowed to use state-operated sewage plants, but an exception was granted to the two camps because of their service orientation, a state official said.

The agreement apparently resolves a 10-year delay that has stymied expansion of the two camps, which are located about 80 miles south of Washington in Scotland, Md., a city of about 5,000 that sits on a quiet peninsula. Stretched along the riverbank near cornfields, pastures and quaint homes, the camps are within a short drive of scenic Point Lookout State Park where the Potomac and Patuxent rivers and the Chesapeake Bay merge.

For about a decade the Distict government has been unable to develop the camp's additional 217 acres of rural property because there was no available sewer connection.

"It's been a major accomplishment for us to get this moving, because it's been debated for 10 years and we have not been able to build on the camp site," said Alexis Roberson, head of the District's recreation department, which operates one of the camps. The Metropolitan Police Boys and Girls Club runs the other.

Installation of the new sewer line means that by the summer of 1986 the city can entertain about 250 children a week at the camp instead of the present 100 a week, Roberson said.

"We can now put up bathhouses and an administration building and have a year-round camping program" instead of the current 10-week program, she added.

The city had set aside $2.1 million for the camp's development, but inflation eroded the value of that money during the stalemate. As a result, development plans no longer include a swimming pool, lighted tennis courts and a dock, although the camp is at the water's edge, Roberson said.

Twelve new cabins were built this year, she said.

While D.C. officials are delighted with the agreement, residents of this small southern Maryland farming community are up in arms over the decision because citizens will not be allowed to hook up to the plant.

In summer the sewage treatment plant serves facilities used by upwards of 1,400 campers a day at the Point Lookout State Park, along with local beach buildings and boat marinas.

But even at the height of the tourist season, the plant processes only 25,000 gallons of sewage a day, a tenth of its 250,000-gallon capacity, state officials said. The camps will generate an additional 30,000 gallons a day, they said.

Some residents also would like to be able to tap that excess sewage capacity. But while the state board of public works granted an exemption to the camps in allowing them to hook up to the plant, it has denied the residents' request, saying it is the county's responsibility to provide sewer service.

County officials say they cannot adequately document the local need for expanded sewage facilities but are working with residents to explore alternatives to sewage disposal.

The final plans for extending sewer lines to the camps were approved by state and county commissioners in August.

George Keller, project manager with the office of environmental programs in the state health department, said the 1,022 houses in the 14-square-mile area could be accommodated without taxing the plant.

Residents disagree. "The idea that federal money is being used to grant sewage privileges to outside interests without changing our status quo is appalling," said Richard Metz, an employe at the Patuxent Naval Air Station and a resident of Scotland.

"It's taxation without representation," said Bud Ridgell, of Scotland Beach.

A study done by the state in 1982 indicated that the septic systems used by nearly all the houses here pose no significant health problems, a finding the residents contest.

Along with about 100 other homeowners on this scenic peninsula, Ridgell reports that his septic tank overflows and run-off becomes contaminated when the rains are heavy.

Despite their interest in hooking up to the state-run sewage facility, some residents of Scotland and nearby Rodo Beach remain staunchly opposed to growth or anything else that might contribute to changing the rural quality of life in the area, such as new sewer line that would stimulate new developments.

Like much of southern Charles and Calvert counties, this southernmost tip of St. Mary's County has been under a building moratorium for 13 years because of the sewage disposal problem.

"I don't want another Ocean City down here," said Wally Scruggs, a retired federal government worker who moved to Rodo Beach six years ago. "I just want to maintain the tranquility without big-city hubbub and the crime that comes with it."

Others argue that health and ecological concerns far outweigh the negative effects of any development that may result if sewer connections are allowed. "If there's effluent washing from houses, down gulleys and into the bay, it's defeating the whole purpose of the governor's bay clean-up project," Metz said.

"Why should those D.C. camps be allowed to expand with their new sewer hook-ups when we can barely survive as a community?" asked W. B. Peterson, a builder who has lived in Ridge for 25 years.

For its part, the state said the county could never prove that failing septic systems in Scotland and Rodo Beach pose a health hazard or create an overwhelming need for sewage collection, said Keller, the project manager.

"Whereas failures at the D.C. camp were massive," septic surveys of Scotland and Rodo beach homes were inconclusive, Keller said.

But Edward Cox, administrator for St. Mary's five commissioners, said the state survey, a requirement for federal funding, was done in the winter, when rains are lighter and runoff problems not as serious.