The EPA has proposed new standards that would sharply reduce emissions from new gasoline and diesel-powered marine engines.

Beginning in 1998, the EPA will require marine engine manufacturers to begin phasing in, over a nine-year period, cleaner-burning boat engines and motors for self-propelled water skis and sleds.

The new pollution controls will add 10 percent to 15 percent to the price of a boat engine, the EPA estimated, but the agency said boaters will save money from a 30 percent increase in fuel economy and improved performance.

About 12 million marine engines are in use around the United States, including about 400,000 boats in the Chesapeake Bay.

Marine engines are major sources of hydrocarbons and nitrogen oxide exhaust emissions. Among “non-road” engine and vehicle emissions, only lawn mowers emit higher levels of hydrocarbons and only farm and construction equipment emit higher levels of nitrogen oxide, according to a 1991 EPA study.

Estimates of the amount of pollution that boat exhaust contributes to the Bay were not available. But nitrogen oxides that result from fossil-fuel burning are considered to be a major source of nutrients to the Chesapeake Bay, contributing an estimated one-third of the total amount of nitrogen that enters the estuary each year.

Besides adding to the Bay’s nutrient problem, hydrocarbons and nitrogen oxide contribute to ground-level ozone pollution in the summertime. Ozone irritates the human respiratory system causing chest pain and lung inflammation. Ozone can also aggravate existing respiratory conditions such as asthma.

The EPA proposal, which is expected to be final in about a year, calls for cutting hydrocarbon emissions from marine engines by 75 percent by 2006 and also cutting nitrogen oxide pollution by about a third.

A long lead time is being proposed to avoid requiring boat owners to scrap their dirtier engines. The EPA estimates it could take 20 years or more to replace all the currently used boat engines with less polluting ones.

“We're not forcing anybody to give up their old boats,” said Mary Nichols, who heads the EPA's air quality programs.

Anticipating the EPA action, marine engine manufacturers have been developing cleaner motor technology.

One improvement has been to replace two-stroke engines with a design that has a direct fuel injection system, so that fuel is sprayed directly into the cylinders, providing improved fuel burn. Manufacturers also are redesigning four-cycle engines to make them less polluting.

One of the biggest manufacturers, Outboard Marine Corp. of Waukegan, Ill. maker of Johnson and Evinrude motors — said it is spending $100 million to change its products to low-emission designs within 10 years. It plans to introduce its first cleaner-running motors late next year as 1996 models, two years ahead of the EPA schedule.

Brunswick Corp. of Lake Forest, Ill., maker of Mercury outboards, said it is working with Chrysler Corp. on a direct fuel injection system for its motors.

EPA’s proposal continues an effort to reduce emissions from “nonroad” engines which include everything from lawn mowers and chainsaws to farm equipment and construction machinery.

Earlier this year, the EPA announced new emissions standards for lawn mowers and other garden and utility equipment. It also has required pollution controls on off-road vehicles used in agriculture and construction.

Car and truck emissions, by contrast, have been regulated for 20 years, and further reductions in their emissions are increasingly costly. The Clean Air Act Amendments of 1990 required the EPA to examine the amount of pollution caused by nonroad emissions.

That study, completed in 1991, found that nonroad emissions were larger than previously thought. An outboard motor, the study found, could generate as many volatile organic compounds — another component of ozone — in one hour of use as a car driven 800 miles.

Hydrocarbon emissions from nonroad sources contribute 10 percent of the urban summertime total, and recreational marine engines contribute about one-third of the nonroad total.

Nonroad engines contribute even more — 17 percent — of the nitrogen oxide total. Of that amount, marine diesel engines contribute 14 percent of the nonroad total, second only to construction and farm equipment.

About 500,000 to 600,000 marine engines are sold annually, according to the National Marine Manufacturers Association.

According to the EPA, these boats, with engines ranging as large as 600 horsepower, spread 700,000 tons of hydrocarbons and nitrogen oxide into the air each year. A typical 50 horsepower marine engine releases 3 pounds of hydrocarbons into the air per hour, the agency said.

Also, studies have shown that as much as a third of the gasoline that goes through many of the two-stroke boat engines does not burn, and is released into the water. Most of that gasoline evaporates into the air.

The EPA requirements will apply to any marine engine of 600 horsepower or less. Most of these engines are designed for recreational boats, although a few might be found on commercial vessels, such as small lobster, shrimp or fishing boats.

The Associated Press contributed to this report.