Representatives of several public health, environmental, and manufacturing groups met last week with the Bush administration’s Office of Management and Budget and asked that more testing be done on car engines before federal ethanol limits are changed, warning that the impact of such an action upon consumers and the environment is not yet fully known.

The question of whether cars can safely run on higher blends is a murky one. At the moment, federal law allows gasoline used in regular cars to contain no more than 10 percent ethanol. The ethanol industry says the proportion could go higher—to 15 percent or even 20 percent—without significantly affecting how cars drive or hold up or how their emissions control systems perform. Some industry representatives are asking the Environmental Protection Agency, which has final say in these matters, to quickly approve 12 or 13 percent blends.