The Environmental Protection Agency is planning new emissions standards for lawn equipment that would cut air pollution and save gas. But manufacturers say the rules could increase the risk of fires and lead to higher prices for consumers.

The new standards would affect all lawn mowers. Currently, there are 52 million residential and commercial mowers (both the ones you push and the ones you ride) and other large lawn equipment that the EPA estimates are in use nationwide. Such lawn equipment is operated about three billion hours a year, the agency says, and a typical push mower emits as much hourly pollution as 11 cars, with a riding mower emitting as much as 34 cars.

To control emissions, lawn equipment would likely need catalytic converters, devices that manufacturers and fire safety advocates say could increase the risk of fires and burns. An EPA safety study released earlier this month, however, found no risk from adding the devices to engines in lawn mowers.

The move toward tighter regulation comes at a time when the landscape industry is booming: Residential lawn and garden equipment, supplies and services generated sales of $24 billion in 2004, up 5 percent from 2003, according to the most recent data available from Packaged Facts, a division of New York-based MarketResearch.com. It also comes during a period of intense industry innovation.

So-called zero-turn riding mowers, for example, a type of rear-engine machine that can turn in place, are able to make grass-cutting more efficient. Manufacturers are also launching a wave of bigger, more sophisticated mowers (which also guzzle more gas than push models). The Bloomington, Minn.-based Toro Co. recently unveiled a new tractor with cruise control. MTD Products in Cleveland this year rolled out its biggest mower yet under the Cub Cadet brand: It weighs 843 pounds and is designed for properties of six acres or larger.

The EPA has not formally proposed the new emission standards, but officials say a preliminary version of nationwide rules should be published this fall. They will likely be similar to those created in California. The California rules ban tanks and hoses made of gas-permeable materials like plastic, which can allow fumes to evaporate, and set strict limits for hydrocarbon emissions, the building blocks of smog. The California regulations are expected to go into effect in January.

"Given the fact that across the country we have areas that have unhealthy air, and localities and states are looking for strategies to reduce smog, we believe it is very appropriate to look at these (lawn-equipment) sources," said Margo T. Oge, the EPA's director of transportation and air quality.

Small engine manufactures say tighter standards will require costly redesigns. The Wauwatosa, Wis.-based Briggs & Stratton Corp., the country's biggest maker of engines for outdoor power equipment, estimated that the California regulations would raise the retail cost of lawn mowers by 31 percent, and said expenses associated with upgrades could force them to move plants overseas. The EPA estimates that adding converters could cost $8 per engine. The retail cost of mowers is around $100 to more than $10,000 for large, riding models.

Opposition to tighter standards from Sen. Kit Bond (R., Mo.), whose state is home to factories owned by Briggs & Stratton, delayed the EPA's emission rules when he called for further study of possible fire and burn risks associated with pollution-control devices in small engines.

The central concern is the catalytic converter, a device used for decades in cars that filters emissions and can generate high levels of heat. The converters have long had fire-safety advocates urging drivers not to park on dry grass or underbrush due to safety concerns, "but you can't tell someone to keep a lawn mower off the grass," says George Miller, chairman of the International Consortium for Fire Safety, Health and the Environment, a nonprofit group devoted to fire protection. The group is working with manufacturers to do their own safety study, to be completed at the end of the year.

Under any new guidelines, the EPA won't specifically ask companies to install catalytic converters in their equipment. But the devices are one of the most effective ways to reduce smog-causing engine emissions.

The EPA's safety study found if systems are retooled to allow for cool air to flow through them, small catalytic converters can successfully be installed in lawn mowers without elevating the risk of fire. The study looked at roughly 60 different engines and 30 types of catalytic converters, and found that temperatures in the equipment could be the same or cooler than current models that don't use the devices. Use of a catalytic converter can cut small engine hydrocarbon emissions by 35 percent, EPA officials say.

Some companies are already moving toward more environmentally friendly products: This year's line of riding mowers from Deere & Co.'s John Deere, which include a fully enclosed engine to mitigate noise and seats with better lumbar support, were also upgraded to include nonpermeable fuel lines to keep gas from evaporating.

A few manufacturers are also offering electric mowers. These are quieter, use only several dollars a year worth of electricity, and don't require engine tune-ups or oil changes. But because they need cords and batteries they are practical only for smaller lawns. Black & Decker, for example, makes the MM875, a 19-inch blade, electric mower that sells for $249, and a cordless version priced at $449. Other alternative mowers don't need gas or electricity, but trim grass by push-power only.

America's obsession with manicured lawns has created a backlash in many areas of the country, as municipalities have restricted the use of mowers and other lawn equipment, such as leaf blowers, because of pollution and noise concerns. Palo Alto, Calif., banned gas-powered leaf blowers in July, and a new ordinance in Pound Ridge, N.Y., prohibits use of commercial landscaping equipment on Sundays. Other cities have incentives to cut down on gas-powered equipment. Fort Collins, Colo., offers a $15 rebate for mowers that are electric or motor-free.

Some consumers welcome the crackdown. Gene Lottner, a 56-year-old comptroller in Stamford, Conn., says he is frequently bothered by the noise and fumes from commercial lawn companies in his neighborhood. If lawn equipment is being used next door, "I can smell it if I have the windows open," he says.

Pollution and noise aren't the only drawbacks to the greater use of lawn equipment. According to the Consumer Product Safety Commission, hospitals saw 14,607 injuries from riding mowers in 2004, up from 9,001 in 2002. There was also an increase in injuries associated with walk-behind mowers: There were 3,485 in 2004, up from 2,450 in 2003.