The federal Environmental Protection Agency is pressing ahead with efforts to tighten air-pollution controls on heavy trucks, diesels and 'super' suburban vans despite industry protests.

The EPA hopes to make the rules final by year's end, thereby toughening standards on trucks and sport utility vehicles, which have less stringent pollution controls than automobiles have.

At the only national hearing on the issue, yesterday in Philadelphia, representatives of the auto and engine industries pleaded for more time.

"We aren't saying we can't do it," said Jed Mandel, a spokesman for the Engine manufacturers Association. "We just need reasonable time."

Environmentalists and air-quality officials, however, urged the EPA to quicken its pace.

"There is probably no more visible or offensive kind of air pollution than the thick, noxious, suffocating exhaust from big diesel trucks and buses," said William Becker, director of the Association of Local Air Pollution Control Officials.

Gasoline and diesel heavy trucks account for about 15 percent of the nitrogen oxide pollution nationally; in some urban areas, such as New York City, that climbs to 50 percent.

"All we are asking the industry to do what it has already said it can do," Said Margo Oge, director of the EPA Office on Mobile Sources.

Driving the new regulations is a legal agreement struck last year between seven diesel-engine makers and the Department of Justice.

The manufacturers were charged with adding a device to their engines that enables them to illegally pass emissions tests.

While maintaining their innocence, the companies - which include Caterpillar, Mack Trucks, Volvo Trucks and Navistar - agreed to pay nearly $1 billion in fines and to support new programs.

They also agreed to make improvements in their engines by 2002 that would cut nitrogen oxides and hydrocarbon pollution. And said they would add new "on-board" diagnostic equipment to monitor engines.

Oge said that EPA was merely turning that agreement into a rule for the entire industry, giving it a 2004 deadline.

The proposed rule would also close a loophole that has allowed SUVs of 8,500 pounds or more to meet pollution standards for trucks instead of automobiles.

EPA officials said this rule would be just the first step in tightening the rules for trucks, and buses. Additional requirements, including cleaner fuels, would be targeted for 2007.

Oge said that the goal was a 90 percent reduction in particulate pollution and nitrogen oxides.

The most straightforward testimony came from Meggy Bechis, a 10-year-old from Yardley who suffers from asthma. "I want the EPA," she said, "to stop trucks and buses from putting bad things into the air."