A proposal to use Fort Belvoir as a regional center for converting trash into usable energy has lost some steam because of opposition from Army brass at the base in southern Fairfax County.

Fairfax officials have proposed that part of the base fronting on Pohick Bay could be an excellent "resource recovery" site because trash and sewage sludge -- the raw materials such operations use to produce steam, electricity and compost -- could be barged there from the Potomac River.

An Army source at the fort said, however, that military officials don't agree. "We don't consider the land (under consideration) to be excess," he said. "It is a prime training site."

Fairfax officials, who have met twice with Secretary of the Army Clifford Alexander, say they remain confident about the proposal, however.

"We think it will work out," said one county official who is familiar with the preliminary negotiations. "The decision will be made at Army headquarters in Washington, not at Belvoir."

Alan J. Gibbs, assistant secretary of the Army for installations, logistics and financial management, confirmed "that the folks at Belvoir do ant to use the area for training. But we want to be as cooperative with the District and Fairfax as we can, and have asked for a thorough review of training requirements at the base."

Even if the Army gives a go-ahead, Gibbs said, other use of the Belvoir land would require congressional action.

Fort Belvoir is one of several places regional officials are studying as potential sites for what they hope will be the wave of the future in waste disposal. Fairfax and District officials have taken the lead in trying to move the region away from conventional disposal systems, such as landfills, to newer ways of handling trash that emphasize the recycling of wastes into useful products such as steam, electrical power of compost.

In Europe, where fuel and power have always been costly, resource-recovery waste systems have been fairly well established for more than 20 years. In the United States, which has enjoyed relatively cheaper energy, the use of such methods has been spotty.

In this region as in most parts of the country, local governments have chosen to dispose of wastes by conventional methods, burying trash in landfills and dumping sewage sludge into trenches.

Local officials now say the area is running out of land for waste disposal, so the idea of resource recovery has become more attractive. Advocates say such an operation could benefit the area in two ways: by providing a way to dispose of the thousands of tons of waste generated daily, and by producing saleable energy.