The Environmental Protection Agency has proposed levying fines of $70,000 against the company that operates Fairfax Connector buses because pollution control devices were removed from most of the fleet, agency officials said.

Fairfax Transit Co., which operates and maintains the buses under contract to Fairfax County, allegedly violated the Clean Air Act by removing the devices from 28 of 33 buses inspected by EPA investigators in November, said agency spokeswoman Martha Casey.

Fairfax County owns the 50-bus fleet but is not expected to share liability for any fines imposed, said County Executive J. Hamilton Lambert. "I don't believe we're liable because most of our contracts require the contractor to follow all federal, state and local laws," he said.

Fairfax Transit mechanics removed the devices to improve bus performance and did not realize it was against the law, said Galen Larson, a senior vice president of National Transit Services Inc., the Chicago-based parent company.

Larson said Fairfax Transit replaced the devices after learning it was violating the law and cooperated fully with the EPA probe.

"It's outrageous" that EPA would propose the maximum possible fine, $2,500 for each of 28 violations, Larson said. "I just think this is terribly unfair."

EPA's "normal practice" is to propose the maximum penalties, said agency attorney Marc Hillson. EPA allows 90 days for negotiations for out-of-court settlement that could lower the fines. Hillson said EPA would "take into account" the company's corrective action and cooperation.

If no settlement is reached, EPA would ask the Justice Department to file a civil complaint against the company, Casey said.

The devices involved, called throttle delay valves, retard the flow of diesel fuel into the engines of the 2 1/2-year-old, 35-foot-long Orion buses, built by Bus Industries of America.

The mechanics removed the valves after having problems starting the engines in the winter, when low temperatures cause diesel fuel to thicken and flow poorly, Larson said.

The valves reduce diesel exhaust, which "is of special concern because of its possible carcinogenic effect," EPA said in a statement.

Fairfax County is "very satisfied" with Fairfax Transit, which has provided Fairfax Connector service since it started in September 1985, said Shiva K. Pant, director of the county Transportation Department.

The county uses the service instead of Metrobus on certain routes in the Huntington area to save money, Pant said.

The county subsidizes Metrobus and Fairfax Connector services, paying the difference between fares and costs, but is saving about $750,000 a year with the Connector because of Metro's higher labor and overhead costs, he said.

Fairfax Transit uses no county employees, provides the service for a fixed fee, and submits maintenance and operating records to the county. But the county does not monitor the company to check maintenance.

"We have no way of knowing" if a pollution control device has been removed from an engine, Pant said.