They're burning garbage in central Baltimore, but you wouldn't know it from the looks of things.

Towering above I-95 as the highway comes into the city from the south stands a 315-foot-high smokestack, its flashing strobe lights and bright perpendicular "BALTIMORE" lettering now a familiar addition to the city's skyline for incoming motorists.

The stack is part of a mammoth and architecturally dramatic waste-to-energy conversion plant that burns up to 2,250 tons of household trash each day and converts it into 60,000 kilowatts of electricity per hour, enough to light 40,000 homes. The $254 million facility was designed by Signal Environmental Systems of Hampton, N.H., which operates it and four others elsewhere.

Officially opened in May, the sleek and almost odorless plant is one of a growing number of high-temperature, mass-burning conversion facilities across the country but the only one operating in the Washington-Baltimore area. Similar but smaller plants are under construction in Alexandria and Portsmouth, Va.

Builders and designers of the Baltimore plant, called the Refuse Energy Systems Co., or RESCO, are confident of its now well-tested technology and its acceptance on the urban landscape.

"We're doing even better than we expected," said plant general manager George T. Hudnet.

"We want it to be the cathedral of garbage plants," said Robert Schoenhofer, executive director of the Northeast Maryland Waste Disposal Authority, the quasi-public agency charged with helping new plants set up in the area.

Leaders in the waste disposal industry see such plants as the wave of the future, gradually replacing traditional landfills and urban incinerators with largely pollution-free technology while doubling as power generators.

Baltimore RESCO, operating on a projected budget of $11 million for the first year, is built to take up to 3,200 tons of assorted residential and commercial trash every day, seven days a week.

Trucks trundle into the plant's receiving area day and night, bringing an average of 900 tons every 24 hours from Baltimore City, 300 tons from Baltimore County and another 300 tons from Philadelphia. ("Philadelphia needed a place to dump their trash," Hudnet explained. "They got thrown out of New Jersey, so they came here.")

In addition, private contract haulers bring in 800 to 1,700 tons of commercial debris daily, everything from Styrofoam cups and hamburger wrappers to construction timbers and discarded television sets. ("I don't like anything bigger than refrigerators," says Hudnet.)

The dimensions of the plant are gargantuan. Two circular windows, each measuring 40 feet across, help illuminate the receiving area. Trucks dump their trash into a concrete pit that is 100 feet deep and 200 feet long.

Huge, electronically controlled steel-toothed buckets like metallic vultures swoop down into the trash, scoop up 2 1/2 to 3 tons at a time and dump it into one of three furnaces, each 30 feet wide.

Temperatures in the perpetually burning fires reach 2,500 degrees. Mountains of flames rage inside, reducing everything but the toughest metals to ash.

"If you've ever seen Hell before, that's it," said Hudnet, peering through a fireproof glass aperture into the inferno.

Massive boilers above the furnaces produce superheated steam. The steam drives a Swiss-made turbine generator, which in turns produces electricity.

About 56,000 of the plant's 60,000 kilowatt-hours are sold to the Baltimore Gas & Electric Co. for distribution to area homes. The remaining 4,000 are used to light the RESCO plant itself.

The emissions coming out of RESCO's smokestack are largely pollution-free hot gases from the boilers, Hudnet said. "At 2,500 degrees, the fires are so hot we have no cancer-causing dioxin problems," he added.

Out of the 2,250 tons of solid waste burned each day, only about 5 percent is left in the form of ash and metals. The metals are trucked to a scrap dealer in New Jersey for recycling, Hudnet said, and the ash is used instead of dirt to spread over raw garbage at one of Baltimore's landfills.

The entire operation is monitored from a control room where engineers seated at a console keep an eye on five computer screens displaying color-coded schematics of various parts of the system. "There are 992 different alarms to alert us to any problems," Hudnet said.

While Baltimore RESCO is willing to receive just about any kind of trash or garbage, there are limits, Hudnet said: "No tires, no waste oil, no sheet rock -- it has sulphur that can create suphur dioxide and acid rain -- and no hazardous biological or infectious wastes."

He said RESCO workers occasionally intercept forbidden materials, and trucks known to haul trash from hospitals are checked periodically for dangerous chemicals or infectious materials.

The 65-employe RESCO plant is similar to four others that Signal Environmental Systems has built in New York, Massachusetts and Florida. Construction of the plant here was financed by $63 million in equity capital from Signal and $191 million in industrial revenue bonds issued by the Northeast Maryland Waste Disposal Authority.

Baltimore RESCO claims one additional bonus for the area. Water drawn from the nearby Patapsco River to cool the plant's generator is siphoned off into two circular ponds before it is returned to the river. The ponds are stocked with 3,000 baby rockfish.

"They're about five inches long now," Hudnet said. "When they get to nine inches, probably next spring, we'll release them into Chesapeake Bay," thus helping to replenish diminished stocks of the fish.