A report by environmental officials from eight Northeastern states is calling for the gasoline additive MTBE to be phased out within three years because it pollutes waterways. Coupled with similar recommendations made by a federal commission last month, the report puts increased pressure on Congress and the EPA to curtail use of the additive. Still, the report acknowledges that getting rid of MTBE, which causes gasoline to burn more cleanly, could pose other health risks by increasing air pollution.