Tempers are smoldering once again in Montgomery County over where the community should burn or bury its trash when its only operating garbage dump is full.

Among those who do not want rubbish dumped near their back yards are residents of Rockville, the Shady Grove area and, most recently, Potomac Electric Power Co. Pepco has a plant in Dickerson, and county officials were hoping that the utility would be willing to burn trash as fuel.

But Pepco last week turned down a proposal to burn solid waste, and county officials and angry citizens groups are scrambling to find a new dump site.

"The county hadn't thought about what would happen if Pepco dropped out," said Jean Cryor, president of Safe Action for Future Environment (SAFE), a 1,000-member citizens group.

"We have two very poor solutions, now that Pepco says they're not in the garbage business," Cryor said.

Pepco had been conducting a test at its plant in the northwest corner of the county to determine the feasibility of producing steam by burning coal together with trash that had been converted to "refuse-derived fuel."

After four months of experimentation, Pepco officials determined that while trash could be burned there and meet the state's emission standards, the plan was technically unsound and jeopardized the reliability of its power output.

"We would have liked to help the county," said Paul Dragoumis, Pepco senior vice president. "But the tests basically failed on the grounds that much new capital investment and technical risk would have been involved."

So it was back to square one for county planners, who have been studying and arguing about the area's garbage for years. By July, the county will have spent $2.8 million on its current solid waste study, and by the end of the decade it will spend an additional $4 million.

The two major sites that county officials will now consider are a landfill at the Travilah Quarry and a "mass-burn incinerator" at the Shady Grove transfer station, where the county's garbage is first collected.

The Oaks landfill in Laytonsville, the county's existing dump, won't be filled for about three years, but Montgomery County Executive Charles W. Gilchrist has set early May as the deadline to find a second site, because officials predict it will take five years to begin operating a new dump.

"Time isn't on our side," said Stewart McKenzie, environmental adviser to the County Council. "There is a great sense of urgency."

Officials of the county's Environmental Protection Department say the 250-foot-deep Travilah Quarry, located between Rockville and Gaithersburg, could be used as a landfill for about 50 years.

"We feel that the quarry is a very viable option," said Bradley Hilton, an engineer with the county's department of environmental protection. "It's a very environmentally safe and sound site for a landfill."

Not so, say residents of the upper Potomac area, who worry that using the quarry as a dump would increase truck traffic and noise and could lead to groundwater pollution. They fear that dumping garbage in the quarry could result in a "Love Canal" that would contaminate the area's ground water.

"It is an absolute danger to the water supply of this area and also D.C. because it is so close to the Potomac" River, said Cryor after a crowded annual village meeting in Potomac last week. "It would be the largest dump in any populated area across this country."

County officials say they are studying a design that would prevent contamination of ground water by garbage. But neighborhood activists contend that the design is faulty and that to prevent contamination, the quarry -- which would be filled with millions of bricklike blocks of solid waste -- would have to be pumped of water continuously. The county would have to get a landfill license from the state to operate at Travilah. But state officials also are concerned about the site because of its potential for ground-water pollution.

The second major option the county is considering is a "mass-burn" incinerator that could handle all kinds of trash and garbage at the Shady Grove transfer station. This plan also faces stiff opposition from Shady Grove activists worried about hazardous emissions from the facility.

"We are very concerned about the hazardous dioxins, lead and hydrocholoric gas emitted from mass incinerators across the country," said Peggy Erickson, president of Concerned Citizens and Scientists for a Healthful Environment, a group with about 10,000 members from the greater Shady Grove area.

"If hydrochloric gas eats paint from the metal on your car, think of what it's doing to your lungs," Erickson said.

Enlarging the current Laytonsville landfill is another option. But when that dump, located seven miles from the Shady Grove transfer station, was opened four years ago to handle all of the county's refuse, nearby residents were promised that it was temporary.

A final option -- and perhaps the most promising, according to county officials -- is burning the trash in a mass-burn incinerator on the grounds of Pepco's Dickerson plant. County officials began studying this option last week, after Pepco's refusal to burn trash at its plant as fuel.