The adoption of the rule on garbage trucks will require 12,000 trash trucks statewide to begin replacing dirty, old engines or fitting trucks with anti-soot devices beginning in December 2004. They will have to complete the task by the end of the decade. The changes should result in a nearly 85% reduction in soot produced by those engines. That, in turn, will lead to less smog and haze.

The action marked the first time that state air quality officials had targeted heavy-duty diesel truck motors in use on highways and at construction sites. While regulations are in place to require manufacture of clean, new diesel engines and fuel, the measure the state Air Resources Board approved this week is the first in the nation to require fleets of existing diesel-powered trucks to begin employing advanced pollution controls.

"These vehicles are in everyone's neighborhood, resulting in direct, near-to-people exposures" of harmful diesel exhaust, said Catherine Witherspoon, the board's executive officer.

Diesel engines are a major source of haze-forming particles and emissions that cause ozone, the main ingredient in smog. But these engines have not been subject to as strict emission-lowering requirements as gasoline engines.

Without deep cuts in diesel exhaust, air quality officials say, it is unlikely smoggy regions like Los Angeles and the San Joaquin Valley will be able to meet air standards mandated by the Clean Air Act.

Kevin Mullins, controller of Mill Valley Refuse Service, said the rules would impose excessive costs on the small, waste-hauling business, which has 40 trucks and has operated in the Bay Area since 1906.

"This could potentially bankrupt our company," Mullins said. "This is a family's life savings that someone is risking on a technology that's not exactly proven."

Jed Mandel, president of the Engine Manufacturers Assn., called the regulation "seriously flawed" and urged the air board to replace it with a voluntary program. The association represents the nation's biggest diesel engine makers, including Caterpillar, Cummins, Detroit Diesel and International Corp.

But air quality officials and even some big waste companies said the rule was one of the most cost-effective measures the air board had recently considered. While the new measures will cost trash haulers about $154 million over the next 20 years, ratepayers can expect to pay about $1 more per year for refuse service over that time to offset the cost of low-polluting trash trucks, according to the air board.

"We support the rule. This is a very cost-effective measure," said S. Kent Stoddard, vice president of Waste Management Inc., which operates about one-third of the trash trucks in California. "This is a big leap of faith for all of us but this is a good rule."

Many of the technologies the air board is prescribing for trash trucks have been in limited use in trucks operating in Los Angeles County for three years. Frank Caponi, supervising engineer for the Sanitation Districts of Los Angeles County, said about 360 trucks fitted with soot-catching filters performed well during tests. In other parts of the state, school and transit buses also have begun to reduce their emissions using similar technologies.

The air board estimates that the changes will eliminate 2.3 million pounds of soot in the air over the next 17 years. Air board officials say those reductions will save the lives of 80 people who otherwise would contract fatal forms of cancer.

A government study by the South Coast Air Quality Management District several years ago ascribed 70% of the cancer risk in air pollution to diesel exhaust. The state declared the pollutant a toxic air contaminant in 1998 and has been developing new measures to reduce the hazard. In coming months, the air board is scheduled to consider additional exhaust controls on diesel engines in fuel tankers, refrigeration trucks and public fleets of cars, trucks and vans.