Washington ? The government is moving on a new front to cut air pollution. This time ferry boats and harbor tugs, farm tractors and train locomotives, and dirt movers at construction sites are the targets.

The Environmental Protection Agency is issuing new regulations aimed at cutting the amount of smog-causing chemicals and fine soot that comes from these off-road, diesel-powered vehicles and machinery.

The regulation, which EPA Administrator Mike Leavitt signed on Tuesday, is viewed by environmentalists and state air pollution control officials as key to meeting federal air quality health standards.

“It is a change that will result in the people of this nation living longer, and living better,” Leavitt said.

He said the agreement represented cooperation among diverse groups including the oil industry, environmentalists, engine manufacturers and state air pollution control officials.

About 159 million people live in areas where smog or microscopic soot is making the air unhealthy, says a recent EPA analysis. The agency cites off-road vehicles used in construction, farming, industrial plants and airports as one reason for the problem.

Those vehicles account for a quarter of all the smog-causing nitrogen oxide and nearly half of the fine soot from mobile sources, according to the EPA.

The EPA regulation, first proposed a year ago, requires refiners to lower the amount of sulfur in diesel fuel for such engines to 500 parts per million by 2007 and to 15 parts per million by 2010. That means less pollution will come out of the tailpipes. Manufacturers also can build cleaner burning engines since the fuel no longer will contain most of the sulfur that damages catalytic converters and other emissions control devices.

Now diesel fuel contains as much as 3,400 parts per million of sulfur.