Automobiles and trucks will cost an addition $1 to 5.50 beginning in 1981 because of new emission control requirements issued yesterday by the Environmental Protection Agency.

EPA Administrator Douglas Costle announced tougher standards for reduction of evaporative emissions - "the hydrocarbon molecules in gasoline vapors" - for 1981-model-year cars and trucks fueled by gasoline.

"These vapors come from the engine itself, gas tank, fuel lines, and other parts of the car," Costle said. "Combined with other pollutants and heated by the sun, hydrocarbons contribute to the formation of health damaging smog."

Costle said the new standard "will reduce nationwide hydrocarbon emissions from all mobile sources by as much as 10 percent in 1985 and 25 percent by 1990.

The move is not expected to have any effect on fuel consumption.

Meanwhile, the EPA also unveiled a mobile laboratory that will enable the agency to test automobile air pollution emissions and fuel economy anywhere in the country.

"The quest to reduce urban smog in this country has focused on the automobile," Costle said. "This new facility will add another dimension to our ability to ensure that cars are meeting federal air pollution standards, both as they come off the assembly line and as they are operated on the road."