Faced with some of the worst air pollution in the country, a grass-roots transit coalition and professors at the Johns Hopkins School of Public Health are urging the state to take steps to reduce the toxic emissions spewed by public buses.

The Maryland Transit Administration should convert its entire fleet of 800 buses to ultra-low-sulfur diesel fuel and add traps for particulate matter and diesel exhaust to the buses, according to a report to be released today by the Citizens Planning and Housing Association.

MTA buses burn 7.8 million gallons of diesel fuel per year, adding to the region's poor air quality and contributing to health problems such as asthma and cardiovascular disease, scientists say.

"If we're going to have public transportation, it should be healthy transportation," said Dr. Michael Trush, deputy director of the Hopkins Center for Urban Environmental Health. "I don't think we should be shortchanging our citizens in terms of health."

It would cost between $5 million and $8 million to add the particulate-matter traps to the buses and an additional $1 million in fuel costs to switch to ultra-low-sulfur diesel fuel, the CPHA estimates. The group says the cost is modest given that the changes would cut bus emissions by 88 percent.

"For a minimal investment, you can make the air a lot cleaner and save a lot of kids from asthma and people from heart attacks," said CPHA transportation director Brent Flickinger.

But a few million dollars are hard to come by at the MTA, which is in the midst of budget cutting.

In a statement, MTA Administrator Robert L. Smith said the agency has formed a clean-fuels working group and is evaluating the use of electric buses on neighborhood shuttle routes.

Other cities, such as Washington and New York, have been more aggressive in pursuing clean fuels, the CPHA said.