WASHINGTON, Oct. 5— Fifteen states east of the Mississippi River are ''extremely vulnerable'' to the harmful effects of acid rain, according to a study released today by the National Wildlife Federation.
The group said its ratings were done by researchers who studied each state's rainfall acidity, soils and water chemistry to estimate potential damage to fisheries, soils, crops and buildings.
Acid rain occurs when pollution formed in the combustion of fossil fuels reacts with water vapor in the air. Environmentalists argue that the problem is getting worse and say tighter limits should be clamped on coal-fired boilers.