Metro officials voted to buy more than 200 diesel and hybrid buses yesterday, reversing the policy of adding natural gas buses and setting off a regional dispute that threatens the system's funding.

After more than two hours of testy debate that seesawed from one compromise proposal to another, Metro board members chose to scrap an $86 million plan to buy 200 natural gas-powered buses and retrofit a garage to service them in favor of using $82 million to purchase 117 "clean" diesel buses and 100 hybrid buses that use diesel fuel and electricity.

Board members Jim Graham of the District and Chris Zimmerman of Arlington County, plus several non-voting alternates, argued that diesel buses are unpopular, that natural gas is the surest way to protect the environment and that hybrids are untested -- fewer than 50 are in use across the country.

Opponents also objected to the hard-line tactics of Maryland's two board representatives, Chairman Robert Smith and Charles Deegan. Both supported diesel buses, and together they had the power to block opposing proposals because any one jurisdiction has veto power when its two members are united.

Smith and Deegan said diesel buses are cheaper and that new technology has reduced their damaging effects on air quality. They also said the best way to cut pollution would be to replace old buses on the street with newer ones.

The decision upends a policy instituted in 2000 to buy only natural gas buses to reduce Metro's contribution to the region's poor air quality. So far the system has spent $160 million to buy 164 buses that run on natural gas and to convert facilities to accommodate them.

Diesel exhaust contains nitrogen oxides and volatile organic compounds that combine to create ground-level ozone, a major component of smog. Diesel smoke also contains toxic compounds and fine particles that lodge in human lungs and have been linked to several health problems.

By contrast, natural gas-burning engines emit almost no toxic chemicals and lower levels of nitrogen oxides, though they do produce higher levels of carbon dioxide and carbon monoxide.

Smith said the environmental differences between the two are negligible and the damaging effects of compressed natural gas buses, also known as CNG, aren't subject to the same scrutiny by the Environmental Protection Agency.

"The interesting thing about CNG is that they emit a bevy of chemical pollutants not cited by the EPA and not regulated," said Smith , who added that Metro's 1,422 buses cause so little of the region's pollution that it doesn't make sense to buy more expensive models.

David A. Catania, a non-voting member of the board who represents the District, said that Maryland's tactics countered board tradition but that "if we're going down that path, every district can play that way."

After the meeting, D.C. Council member Phil Mendelson (D-At Large) said he and other council members, including Catania, were backing a proposal that would prohibit any D.C. dollars from being used to buy diesel buses.

"It's outrageous," Mendelson said. "This is just a step backwards."

Metro officials said last night that they were unsure what effect such a measure would have, but it could lead to reconsideration of the issue because the buses wouldn't be purchased for at least a year.

In 2000, Metro officials pledged to buy natural gas buses, like this one. Their latest vote changes that policy. D.C. Council member Phil Mendelson wants to block funding for diesel buses.