The California Air Resources Board, which convened in Fresno, told Valley air officials to find any possible further restrictions for boilers, food dehydrators, glass furnaces and farm diesel engines.

But the order was too vague, said activists who wanted the plan to be more aggressive.

"We have no idea what pollution reductions will come from them," said lawyer Brent Newell of the Bay Area Center on Race, Poverty and the Environment, which represents Valley activist groups. "We're left with a symbolic gesture but little else."

The cleanup plan for soot, known as PM-2.5, now will be sent to the U.S. Environmental Protection Agency, which is expected to approve it. The plan calls for San Joaquin Valley air to meet the federal-PM 2.5 standard by 2014.

The Valley ranks alongside the South Coast Air Basin with the worst PM-2.5 problems in the state.

PM-2.5 comes from vehicles, fires and other sources of combustion, such as boilers. But the region's biggest PM-2.5 problem is from airborne gases that combine in winter to form chemical specks of ammonium nitrate. Oxides of nitrogen from vehicles, such as diesel trucks, combine with ammonia from dairies to make the specks.

About 30 to 40 of these specks would span the width of a human hair, and they can evade the body's defenses, lodging deep in the lungs. They trigger asthma and heart problems, and they can cause premature death.

A state study discussed at the meeting Thursday in Fresno said the particle pollution is 70% more lethal than scientists previously suspected -- killing an estimated 3,000 Valley residents prematurely each year.

The study added more emotion to the activists' argument against the PM-2.5 plan, which they say relies too heavily on the state's proposed diesel truck rules. The rules, which are meeting resistance from the trucking industry, may get watered down, activists said.

"Send this plan back to be strengthened or do it yourself," said Melissa Kelly-Ortega, program coordinator for the Merced-Mariposa Asthma Coalition. "You will be saving lives."

They made the same objections last month at a meeting of the San Joaquin Valley Air Pollution Control District board. The district board approved the plan on an 8-3 vote.

One of the dissenting votes was the board's newest member, Dr. John Telles, who said he questioned the approach to PM-2.5 monitoring and didn't see enough of a backup plan in case the proposed measures don't work.

Telles is the Valley air district's representative on state board, but he missed Thursday's meeting because of a family commitment out of state. He sent an e-mail that was read aloud at the meeting. It echoed his concerns from the Valley district meeting last month.

Like the Valley air district, the state board is counting on the diesel truck rules. Air board staffers said the new rules, along with existing rules, will bring the Valley's air into compliance with the standard.

Officials added that the PM-2.5 problem already has been reduced through the hard work of the Valley air district. State officials said the region's concentrations of the pollutant have dropped by 45% since 1999.

The northern Valley, with about 40% of the region's population, has achieved the standard for PM-2.5.

"Tremendous progress has been made here," said state board chairwoman Mary Nichols. "In fairness, the district has been doing a good job."

But she noted the concerns of activists and offered the possibility of further pollution reductions on boilers, farm engines, glass furnaces and food processing hydrators -- all of which were among suggestions from activists.

In addition, fireplace-burning restrictions, which the plan will tighten, also could be made more stringent if the Valley's PM-2.5 levels don't drop fast enough, she said.

Activists were not reassured. They said the state should have rejected the plan and sent it back to the Valley air district to add many other restrictions, such as further controls on composting facilities and dairies.