Washington ? The Bush administration proposed reductions greater than 90 percent in air pollution from diesel-powered farm, construction and other off-road equipment Tuesday, predicting the curbs would prevent thousands of premature deaths, heart attacks and respiratory ailments.

The changes would start with 2008 models, and all bulldozers, farm combines and other diesel-powered equipment not used on roads must have modern emission controls by 2014. Cleaner-burning diesel fuel would have to contain 99 percent less sulfur by 2010.

Diesel vehicles are responsible for large amounts of the microscopic soot that causes respiratory problems and smog-causing chemicals from motor vehicles, with construction, farm, mining, locomotive and marine engines the main sources of off-road diesel pollution.

The new engine pollution requirements are part of a broader push by the Environmental Protection Agency to reduce tailpipe emissions from diesel-powered vehicles. The latest proposal builds on a 2001 rule ordering pollution cuts from heavy-duty diesel engines and diesel fuel used in highway trucks and buses.

EPA also has imposed tougher emissions requirements for diesel locomotive engines.

The agency estimates that, by 2030, its latest proposal will prevent 9,600 premature deaths, 16,000 heart attacks and 260,000 respiratory problems in children. EPA worked with the White House’s Office of Management and Budget on the proposal, which is scheduled to be made final next year after a public comment period.

Health and environmental groups welcomed the move, saying that it would dramatically improve public health.

Particularly susceptible to the effects of diesel exhaust are children, the elderly, and people with asthma, cardiopulmonary, lung and chronic heart diseases, according to a report Tuesday by the American Lung Assn. and Environmental Defense.