On the former site of the Kenilworth dump in Northeast Washington, 26 feet beneath a grassy field where rugby teams battle, bacteria in an abandoned landfill are saving Uncle Sam hundreds of dollars in energy every week.

What in the mid-1960s was a smoldering dump is now an abundant source of free methane, the natural gas produced by bacteria feeding on refuse. After three years of studying the practicality of the project, the National Park Service is using the free fuel near the Anacostia River to heat six large greenhouses, facilities at its Aquatic Gardens and two storage sheds.

"It's beautifully efficient," boasted Jim Wolfe, maintenance chief for the park service region that includes the District. "Greenhouses are not efficient structures, especially in the fall and winter."

Heating the greenhouses, which are 150 feet long and 50 feet wide, cost $39,000 in 1981. This year, the cost will be about $14,500. With the cost of natural gas and heating fuel expected to rise in the future, the methane system will pay for its $225,000 cost in 10 years, Wolfe said.

"The beauty of the thing is that the methane won't expire; it never runs out. As long as they have no oxygen, the bacteria are always producing the gas," Wolfe said.

In 1979, the park service started studying ways to get at the methane known to be percolating in the old dump. Scientists from Johns Hopkins University's applied physics lab and park service technicians devised a way to tap the gas.

Getting to the methane was easy: nine plastic pipes, six inches wide and encased in gravel, were sunk 26 to 28 feet into the old dump, which is covered by an airtight, three-foot layer of clay. The wells were capped and joined by 4,000 more feet of pipe. Five-horsepower fans move the gas -- a 3-to-1 mixture of methane and carbon dioxide -- through the pipe to a point where it is cleaned of dirt and moisture.

From there, the gas proceeds to several gas-fired heaters, which blow hot air into the greenhouses, where flowers and shrubs are raised for several federal buildings, including the White House. Though the methane is not as strong as its commercial counterpart, it is adequate, Wolfe said. "We're getting 150 cubic feet of gas per minute," he said.

Innovative energy sources are nothing new to Wolfe, who converted 52 gasoline-powered lawnmowers to ethyl alcohol just before the 1976 gas crunch.

"From now on," he said, "we can't afford to overlook the sources in our own back yard. Pretty soon, cities will be designing landfills to be able to extract the gas out of them."