The Environmental Protection Agency has decided to suspend enforcement of its ban on the gasoline additive MMT for the summer driving season, an action that the oil industry claims will add 340,000 barrels of unleaded gasoline per day to available supplies.

In a meeting with his top advisers yesterday, EPA Administrator Douglas Costle decided to quietly suspend enforcement of the ban for the summer rather than grant a temporary suspension of the ban itself. Costle feared that such a suspension could lead to continuing waivers of the rule, according to sources.

MMT is a manganese-based gasoline additive that was used by refiners until September 1978 to boost the octane rating of unleaded gasoline.

The EPA originally banned MMT because tests showed that the additive increased hydrocarbon emissions from autos using unleaded gas with MMT, and effectively disabled automobile catalytic converters.

Last month Tenneco Inc. filed a petition with the EPA on behalf of a number of refiners asking the agency to officially lift the ban, at least for the driving season, to allow the industry to increase its unleaded gasoline production.

There has also been pressure form the Department of Energy on the EPA to lift the ban and allow increased unleaded production of unleaded.

Costle and other EPA officials expressed fears at yesterday's meeting that such a suspension could lead to the same problems the agency has incurred in its lead phasedown program. after one waiver was granted delaying the lead phasedown, others followed.

But it was clear, for political reasons, sources told the Washington Post, that environmental consideration would have to be forfeited in favor of anything that could increase thr fuel supply during the peak driving months of the summer.

"Suspending of the MMT ban for the summer driving season will increase oil industry profits but will not increase unleaded gasoline supplies," said Clarence Ditlow, director of the Center of Auto Safety. "The oil industry can make just as much unleaded gasoline by further refining as by the addition of MMT."