They're dimming the lights at McDonald's.

Not to mention fiddling with the lights in the meat lockers, metering the water to the potties and installing new, high-efficiency air-conditioning units, all powered by the "pint-sized power plant of the future."

Ten years after the McDonald's restaurant chain and the Environmental Defense Fund teamed up with an agreement that led to elimination of the polystyrene sandwich container, the two are at it again.

Last time the goal was to get rid of tons of waste. This time the object is energy conservation at the 12,500 U.S. restaurant buildings themselves, where the nation's largest fast-food chain hopes to cut energy use by 10 percent. Just when this will be accomplished is still a matter of conjecture, but the folks at the Environmental Defense Fund are hoping to announce a timetable by April, when they celebrate Earth Day 2000.

"It's going to be a several years' process. It's not something you can do in months," McDonald's Chairman Jack Greenberg told a news conference. In many cases, the company will have to wait until the restaurants owned and operated by its independent franchisees need to be remodeled or rebuilt.

"We're constantly remodeling and rebuilding our older restaurants. We can select those things [energy-saving devices] that have the most impact," Greenberg said. But he acknowledged that "we have a lot more control over the new restaurants we build."

Still, Greenberg, said, "we don't think it's going to be a hard sell" persuading franchise owners to get with the energy-saving program.

However it eventually works out, the staff at the Environmental Defense Fund couldn't be happier.

"We see the importance of this announcement in that there will be a commitment to further reduce energy use and another reduction in greenhouse emissions," EDF Executive Director Fred Krupp said at the same news conference.

EDF, along with the Pew Charitable Trusts, formed an alliance with McDonald's 10 years ago after the chain agreed to stop using polystyrene sandwich containers in an effort to eliminate waste. Since then, working through the alliance, McDonald's has taken a number of steps that have saved 150,000 tons of packaging, according to the company and EDF.

The list ranges from cutting an inch off the napkin size and putting hash browns in paper bags to reducing the thickness of sundae cups and cutting the weight of the Happy Meal bags.

The alliance said yesterday that since the end of 1990, when the company first eliminated the polystyrene sandwich boxes, McDonald's has purchased more than $3 billion worth of recycled products and recycled more than 1 million tons of corrugated cardboard.

Greenberg yesterday was unable to say just how much money McDonald's had saved because of the changes.

Burger King, the nation's fourth-largest fast-food chain, said yesterday that it, too, is dedicated to waste reduction, and it described a four-point conservation program aimed at reducing waste and saving energy. The company said the only plastic foam it uses is in coffee cups, and the cups contain no environmentally harmful chlorofluorocarbons.

Since 1991, Burger King said, it has used only paper wraps instead of paper cartons at its 10,000 restaurants worldwide. Burger King said it also was heavily into recycling, is testing a way to compost its waste and is participating in the Green Lights Program in an effort to use energy-efficient lighting.

Other major chains did not return telephone calls seeking comment.

Environmentalists have been focusing their efforts on McDonald's--enough so that they say they know the company isn't just inflating the numbers.

"We are familiar with their suppliers. We know paper issues. We know paper mills and we know the processes from those mills," said Jackie Roberts, director of the alliance for EDF. Roberts said she is a chemical engineer by training and knows "how you make things."

"We do pretty extensive verification. These are all verifiable numbers," Roberts said. And besides, she said, "in terms of the data, we do very much trust McDonald's."

And what about the new energy-saving program the company has been testing at five stores in Illinois, California, Colorado and Georgia?

"We inspected all five stores before we agreed to endorse the effort," Roberts said. "For the service industry, this really is cutting edge."

Janet Abramovitz, a senior researcher at the World Watch Institute, calls the alliance with McDonald's "very fruitful." Abramovitz has just completed a report on efforts to reduce paper waste and said the program at McDonald's has been a leader in the fast-food industry.

As an example, Abramovitz said the conversion from cardboard to paper wrappers for the hash browns resulted in a 90 percent savings in paper use. Taking the embossing off the napkins used in the restaurants produced a 20 percent paper reduction because more napkins could fit in a box for shipping.

Terry Davies, director of the center for risk management at Resources for the Future, agreed that McDonald's is a leader in its industry in the wasted-paper chase. "There is no question they are more environmentally aware than any of the other fast-food chains," Davies said. He said that as far as he knows, none of the other major fast-food chains has gone as far as McDonald's, although some have followed in the leader's footsteps in some areas.

But Davies said there was a lot more McDonald's could do to pressure its suppliers to be more environmentally aware. He noted that while McDonald's is only a small player on the world stage, it is a major player in U.S. agricultural production and food processing. For instance, he said, 5 percent of all potatoes this country consumes are sold by McDonald's.

McDonald's has installed a series of energy-conservation systems at the five experimental restaurants. They range from electronically controllable ballasts to dim the fluorescent lights in automatic response to the amount of daylight, and light pipes in the roof to bring more daylight into the building, to high-efficiency air conditioning, infrared-controlled water valves in the restrooms and an electronic device that automatically turns off the light in the walk-in freezers.

Perhaps the biggest innovation, however, is the 75-kilowatt, natural-gas-fueled TurboGenerator that will serve as the restaurants' own mini-power plants. The generator is part of the new movement known as distributed power to help take the load off the centralized power stations used by electric utilities.

Not bad for an alliance that Greenberg said started 10 years ago with "a controversial foam container and a handshake."

Both McDonald's and Burger King participate in Green Lights, a voluntary energy-conservation program. They say they also have taken these steps:

MCDONALD'S 1990-1999

* Eliminated 150,000 tons of packaging.

* Recycled 1 million tons of corrugated cardboard.

* Reduced 510 million kilowatt-hours.

BURGER KING

* Since 1954, primarily has used paper packing for its products.

* Since 1991, has been using sandwich wrap instead of paper cartons in its restaurants.

* Uses recycled white bags for takeout orders.

SOURCES: The companies