The EPA has approved new rules that would require emissions from heavy-duty trucks and buses to be 95 percent cleaner than those manufactured today.

The rule, issued by the Clinton administration in December, would also require that sulfur in diesel fuel be reduced by 97 percent to help meet the emission target.

The rule would ultimately have the same effect as eliminating air pollution from 13 million of today’s trucks.

“Anyone who has ever driven behind a large truck or bus is familiar with the smell of diesel fuel and the clouds of thick exhaust emissions,” said former EPA Administrator Carol Browner. Because of the new rule, she said, new trucks and buses would run “as cleanly as those running on natural gas.”

The action would also benefit the Bay because it would reduce 2.6 million tons of smog-causing nitrogen oxide emissions a year. Nitrogen oxides from fossil fuel combustion are a major source of nitrogen entering the Bay, and heavy trucks contribute about a third of all motor vehicle nitrogen oxide emissions.

Older, dirtier diesel vehicles can each emit almost 8 tons of air pollution a year, and pose a threat to human health, according to the EPA.

Refiners, though, have vowed to challenge the sulfur reduction requirement in court, and are lobbying the Bush administration to find a way to alter the rule. But the rule has been supported by the auto industry, which argues that the overall emission reductions cannot be met without reductions in the amount of sulfur in fuel, which degrades emission control devices.

Under the rule, refiners would have to meet the fuel requirements by mid-2006, while the new emission standards would take effect in the 2007 model year.