The Environmental Protection Agency has decided to allow continued marketing of gasohol, and experimental and controversial automobile fuel being sold on a limited basis in the Midwest.

The action came in response to a request from Gas Plus Inc. and the state of Illinois to waive a ban on the fuel's use which would have gone into effect today.

Gasohol, which contains 90 percent unleaded gasoline and 10 percent ethanol, purports to offer environmental and energy advantages. It has been on sale in recent months at fewer than 200 Gas Plus stations. Sales have been increasing dramatically in recent months.

Under the Clean Air Act of 1977, certain fuels and fuel additives-including gasohol-were banned last Sept. 15. But the EPA can grant a waiver if it believes that use of the fuel or additive will not cause or contribute to the failure of a vehicle to meet emission standards.

Because sales of gasohol represent only .005 percent of the nation's gasoline sales, EPA administrator Douglas Costle said, "there is no significant enviroment risk associated with its continued use."

Recent EPA and Department of Energy tests have confirmed earlier findings that use of gasohol results in a slight decrease of tailpipe exhaust emissions of hydrocarbons and a significant decrease in carbon monoxide emissions.

The tests also show, however, slight increases in nitrogen oxide emissions and substantial increases in evaporative hydrocarbon emissions.