The Department of Transportation yesterday abandoned a decade-old effort to shorten truck and bus drivers' working hours, saying the relationship between driver fatigue and accidents is not conclusive enough to justify the estimated $11 billion cost of the proposals.

"I think this is the end of the general proceeding looking for an . . . overhaul of the rules," said Kenneth L. Pierson, director of DOT's Bureau of Motor Carrier Safety. "It still may be possible to do some spot fixes."

Under existing rules, the 3 million drivers of the nation's interstate buses and trucks may drive no more than 10 hours after an eight-hour break, and are limited to 60 hours' work in seven days or 70 hours' in eight days.

The abandoned alternatives included maximum eight-hour shifts, a ban on driving between midnight and 6 a.m. (the time of greatest accident risk for truck drivers) and allowing meal breaks during on-duty time.

Bus and trucking companies and large manufacturers opposed the proposals. Drivers were split. Some favored changes, some favored the status quo and some wanted the government to eliminate any regulation potentially limiting their incomes.

Jack Dwyer, chairman of the American Bus Association's safety committee, issued a statement saying, "We're pleased to know they listened to us. The economic costs we would have faced just weren't justified by any increase in safety."

Clark Martin of the American Trucking Association echoed this sentiment. The ATA and other groups contended that increased accidents might result if firms were forced to hire inexperienced drivers.

Consumer activist Ralph Nader's response was, " Transportation Secretary Drew Lewis is unleashing giant tractor missiles driven by overworked, fatigued drivers popping bennies and amphetamines . . . . Companies have the economic incentive to push drivers, and the driver makes overtime, so he has an incentive to push himself . . . . "

Between 1971 and 1978 the Bureau of Motor Carrier Safety commissioned several studies of the underlying safety and economic issues. Two showed that driver errors increased near the end of a 10-hour shift and that a series of long days had a cumulative effect in reducing driver performance.

One showed no consistent relationship between driving hours and the frequency or severity of truck accidents, although fatigue-related accidents were more frequent between 11 p.m. and 8 a.m. Another set a $10.5 billion to $11.5 billion price tag on the proposals, based on increased labor, vehicle and overhead costs.

Yesterday's Federal Register notice cited a $450 million estimate as the proposals' potential benefit, a figure Pierson based on the "anticipated savings of life" because of reduced accidents.