Two consumer groups have sued the Department of Energy in an attempt to block the implementation of amendments to petroleum pricing regulations that could add up to 4 cents to the cost of a gallon of gasoline at the pump.

Public Citizen and the Center for Auto Safety, two groups affiliated with Ralph Nader, have challenged the amendments by arguing that the resulting price increases would cause motorists to switch from unleaded to leaded gasoline, thus increasing air pollution.

Nader joined the suit, which was filed in U.S. District Court here.

The controversial amendments would allow oil refiners to pass through to consumers additional non-gasoline-related costs.

The Nader suit said the DOE action was actually an end run in its efforts to deregulate completely the price of gasoline at the pump, a position the consumer groups oppose.

Because of shortages in unleaded gasoline, its price will continue to rise while leaded gasoline prices will probably stay about the same, the consumer groups contend. Some studies contend that thousands of motorists already have switched to the dirtier leaded gasoline because of the price difference. And the Environmental Protection Agency has contended that continued switching could increase air pollution.