Putt putt: the small gas engine is an environmental nightmare.

Most summer weekends, a few million people use them to mow lawns, trim hedges, blow leaves or cut up firewood. Millions more use them to buzz over waterways and lakes in jet skis or motorboats. In the winter, people in the colder climates roar along snow-clogged residential sidewalks or driveways with them. More than 89 million small gasoline engines, around 25 horsepower or less, are operated in the United States. Another nine million may be in use in Canada.

They're tiny, but when it comes to pollution, the damage they do is far out of proportion to their size. "They're all dirty," says the Environmental Protection Agency's (EPA) Betsy McCabe. "The marine engines are dirty, the small lawn care engines are dirty. They don't produce as many hydrocarbons as cars, but they have a lot of NOX [nitrous oxides] and they have particulates."

McCabe works out of Ann Arbor, Michigan as an Environmental Protection Specialist in the Engine Programs and Compliance Division of the EPA's Office of Mobile Sources. Overall, she says, these engines account for five percent of the total, national summertime level of hydrocarbon pollution in urban air, and about the same percentage of wintertime carbon monoxide levels. But they also contribute up to 20 percent of the pollution in cities.

And the marine environment is damaged as well; pollution from some 12 million two-stroke marine engines like outboard motors, jet skis or personal water-craft, amounts to the equivalent of 15 Exxon Valdez spills each year in American water-ways. These engines leak copious amounts of fuel directly into the water, coating the surface and poisoning the sensitive aquatic food web. This spillage represents as much hydrocarbon pollution as is created by all the cars in the United States.

Of all the "non-mad" engine (not cars or trucks) sources of urban summer air pollution, recreational boats contribute 30 percent, small spark-ignition engines like the lawnmower throw in fully half, and other non-road engines add the last 20 percent.

Until recently, these small engines have gone virtually unnoticed in campaigns to control urban air pollution. Even now, though, there's little attention paid by most environmental or consumer groups to the smaller engines. Or to the alternatives.

The Cutting Edge

That fine, 1950's Sunday-morning serenade of quietly whirring hand-mowers is slowly returning to suburban America. But using hand tools for lawn and garden tasks requires finding the equipment. American Lawn Mower manufactures a range of push mowers, operating on person-power, running from $60 to $130, with added grass catcher for another $25. Its products are available at lawn and garden centers or hardware retailers across North America.

If electric is more your style, the Real Goods Trading Corporation offers the Ryobi cordless rechargable lawnmower, which runs off a 24-volt DC battery. Ryobi's mower ($375) will run for 60 to 90 minutes, and is rechargeable via house current. "This is the best one we've seen," says Mike Sischo of Real Goods product support. "It works really well."

Rechargable electric boats are becoming popular for lake and river use, where range and speed are not significant factors. An example is the French-built Ruban Bleu runabout, whose 420-watt, 12-volt motor can carry it to a maximum of four miles per hour.

Having an Impact

Consumers who aren't ready to make the leap to the electrics can reduce the damage caused by their gas equipment if they follow a few simple rules developed by the EPA:

* To avoid spills, use a small funnel-equipped gasoline container that you can handle easily, allowing slow and smooth pouring into the gas tank;

* Avoid overfilling the tank or allowing fuel to run over. Special nozzles equipped with an automatic stop device make this less likely. Close the cap or spout on gasoline containers tightly after filling, and remember to recap the gas tank on the equipment;

* Regularly change oil and air filters, and use the correct oil grade for the season.

Cleaner Boats

Spurred on by upcoming EPA emission standards for commercial and recreational marine engines, the boating industry is at last developing technology for a new generation of low-emission, high-performance engines. It will be several years before this new technology is available to the public, but there are precautions that boaters can take right now that will reduce the high levels of ozone-affecting hydrocarbons and NOX their pleasure craft emit:

* Limit engine operation at full throttle and cut back on unnecessary idling;

* Transport and store gasoline out of direct sunlight, in a cool, dry place;

* Replace old, worn engines with newer and cleaner-burning models, and prepare them properly for winter storage.

Growing, Not Mowing

Lawns cover over 25 million acres of America, an area the size of Pennsylvania. This green carpet may be pretty, but since World War II, mirroring the rise of suburbs, it has slowly, relentlessly replaced the natural habitat of native plants, animals and birds. And maintaining its manicured perfection is environmentally costly. A gas mower cutting a quarter-acre lawn produces more pollution than a new pickup truck traveling round-trip between Washington and New York. That's why many environmentalists advise homeowners to cut down on lawn area.

The Gardener's Supply Company's Better Gardening Bulletin recommends replacing as much as 80 percent of your high-maintenance grass with stately trees, native shrubs, evergreen ground cover, ornamental grasses and perennials. The Caldwells of rural Knoxville, Tennessee, for instance, have gradually reduced their lawn from five acres to 1/4 acre by planting a vegetable garden and a stand of native white pines, and creating a kitchen herb patch and brick patio.

For that section of lawn that you do keep, the Bulletin recommends mowing high to encourage deeper, healthier roots (which will sustain a lawn through a hot summer); leaving lawn clippings where they fall to feed the soil (or raking them and using them for compost if they're thick and wet); and using slow-release organic fertilizers to encourage moderate growth and less-frequent mowings.

Even if you must keep your expanse of lawn, there's no law requiring that it be gasoline powered. Reverting to ordinary muscle-power is "certainly an option," says EPA's McCabe. In the Washington office of the Sierra Club, Dan Becker says, "We should do what we can do in the short run. Don't have a more polluting mowing machine than you need, run it as little as possible, and keep it tuned up. Consider an electric one that's at least a little bit cleaner. Or plant vegetables instead."

CONTACTS: American Lawn Mower, Great States Corporation, P.O. Box 369, Shelbyville, IN 46179/[phone]; Environmental Protection Agency Office of Mobile Sources, 2565 Plymouth Road, Ann Arbor, MI 48105/[phone]; Gardener's Supply Company, 128 Inter-vale Road, Burlington, VT 05401/[phone]; Real Goods Trading Corp, 555 Leslie Street, Ukiah, CA 95482/[phone]; Ruban Bleu, Quai des Antilles, 44 200 Nantes, France/[phone]-48-74-33; Ryobi Outdoor Products, 550 North 54th Street, Chandler, AZ 85226/[phone].

JUDY WAYTIUK is a freelance writer based in Manitoba, Canada.