The tax benefits are set to expire at the end of the year, but their proponents are already working to renew them.

Most Democrats banded together with farm-state Republicans to defeat the effort by Senator Tom Coburn, Republican of Oklahoma, who along with his allies charged that federal ethanol supports are wasteful and unnecessary and are increasing the cost of food by inflating the price being paid for corn.

“Parochialism trumps the best interests of the nation,” Mr. Coburn said after the vote.

Those who opposed him, while acknowledging that the ethanol subsidies are likely to be eased out eventually, said it would be disruptive to the agricultural and fuel markets to make a sudden change.

“We have a lot of folks who made investments, you have people across the country whose livelihoods and jobs depend upon this,” said Senator John Thune of South Dakota, one of 13 Republicans who opposed the Coburn plan. “I think it makes sense, when we put policy in place and we say it is going to be in place for a certain period of time, that that be honored.”

Some Democrats said they based their opposition to Mr. Coburn’s plan on a procedural move he made to force the vote, saying he had usurped the authority of majority Democrats to control the floor. Senator Harry Reid, the Nevada Democrat and majority leader, said Democrats would be back soon with an alternative proposal.