Six governors, oil refiners and companies hurt by high corn prices have asked the agency to waive its requirements for ethanol and other renewable fuels. Some single out the corn ethanol mandate, but others want the quota for cellulosic fuels waived, too, partly because there is no actual production.

The cellulosic biofuel industry has asked the E.P.A. to keep all the rules intact. Waiving the rule for corn ethanol would discourage investment in advanced biofuels as well, said Brent Erickson, a spokesman for BIO, a trade organization. “You can’t de-link them,” he said.

The agency was expected to rule on Tuesday, but instead said it would rule “shortly.” To grant the waiver, it would have to find severe harm to the economy. Energy experts say that eventually renewable motor fuel could have a much bigger impact on the United States economy than renewable electricity from wind farms or solar cells. Renewable electricity saves coal and natural gas, which are cheap and domestically plentiful. Renewable motor fuel displaces oil, which is much more expensive and often imported, which poses a host of national security and trade issues.

If either Ineos or KiOR began commercial production, it would break a long string of overly optimistic promises made by the industry and the government.

In October 1998, for example, the Energy Department showed off a plant in Jennings, La., that made ethanol from sugar cane wastes; the department said it would reach commercial production within a few years. At the time the plant was owned by a government-subsidized firm called BC International, which was later reorganized and renamed Celunol. Then it was taken over by Verenium, which, with backing from BP, tried another method. BP announced on Oct. 25 that it was dropping plans for a commercial plant based on technology piloted at Jennings, although it still does research there.

Mascoma, based in Cambridge, Mass., and backed by General Motors and Khosla Ventures, among others, is trying to make ethanol from wood waste. Samir Kaul, a board member representing Khosla, confidently predicted in 2006 that it would be in commercial production by 2008, but that goal remains elusive.

Iogen, an established Canadian producer of enzymes, began producing ethanol from wheat straw in 2004, and said in the fall of 2005 that it hoped to announce plans for a commercial plant by the end of that year. Eventually, it announced plans for a plant in southern Manitoba, but in April of this year it dropped that idea, and laid off some workers at its Ottawa headquarters.