The Environmental Protection Agency cleared the way Friday for regulations to limit pollution from lawn mowers, jet skis and similar small machines.

Devices that clean the engines' emissions do not pose a safety problem, the EPA said. Without new pollution controls, engines under 50 horsepower would account for 18 percent of smog-forming emissions from mobile sources by 2020, the agency has estimated.

Opposition from Sen. Kit Bond, R-Mo., whose home state has two factories owned by lawn mower engine maker Briggs & Stratton Corp., has delayed rules to regulate small-engine pollution.

After first trying to bar California from implementing its own small-engine rules, Bond last year insisted on a study of whether adding pollution-reducing catalytic converters to small engines could create fire risks.

The EPA study released Friday concluded there are no such risks and said there can even be safety benefits from adding catalytic converters.

The conclusion means EPA can move forward to issue nationwide regulations for pollution from small engines. The agency also can grant California the waiver it is seeking to implement its own small-engine pollution rules.

EPA spokesman John Millett said the agency should be able to take both steps by the end of the year.

Agency investigations indicate the pollution standards can be implemented "without an incremental increase in the risk of fire or burn to the consumer" and can even lead to "an incremental decrease in such risk," the study said.

"EPA's thorough safety study shows that not only will California's proposed small engine regulations significantly improve our air quality, but they also present no safety concerns whatsoever for consumers and in fact may improve the safety of lawnmowers and other small engines," said Sen. Dianne Feinstein, D-Calif., who has tangled with Bond over the issue for nearly three years.

Patricia Hanz, a spokeswoman for Briggs & Stratton in Milwaukee, called the EPA study "neither comprehensive nor complete" and said the company was waiting for results from a different safety study that includes participation by the Outdoor Power Equipment Institute, an industry trade association.

Briggs & Stratton officials have said that redesigning their engines to comply with tougher regulations would be so costly they might have to move production overseas. The company employs more than 1,000 workers in Missouri.

There was no immediate comment from Bond.

California has the authority under the Clean Air Act to set its own pollution standards, and other states can put in place California's regulations. Bond tried to include language in a 2004 spending bill to block California from setting its own small-engine rules, but Feinstein objected. Bond then agreed to language letting California implement its own small-engine rule but requiring a federal standard to be set for other states.