The White House began reviewing rules Friday that could reduce the use of ethanol and other biofuels, setting off an intense lobbying fight that may not end until after the midterm elections.

The Environmental Protection Agency sent the Office of Management and Budget a long-awaited proposal for review that would set the federal target for blending biofuels into gasoline.

If the proposal follows a draft outlined last fall, the federal mandate would go down from 16.7 billion gallons of blended biofuels this year to 15.2 billion gallons.

The proposed standard will have at most a 90-day review, which would push it comfortably past the Nov. 4 elections. In the meantime, the oil, gas, poultry and livestock industries, which oppose the mandate, will be pitted against biofuel firms.

Environmentalists are torn on the issue, with some arguing that next-generation biofuels could help reduce greenhouse gas emissions. Some environmental groups, however, oppose the use of corn-based ethanol, which they say is worse for the climate than conventional gasoline.

As a senator from the corn-growing state of Illinois, President Obama was a big booster for ethanol during his 2008 run for the presidency and his administration had backed the renewable fuels standard in the past.

But the EPA shocked the biofuels industry last fall when it first proposed cutting the annual blending targets. It's not clear yet whether the final rule sent to the White House will include the proposed cuts or not.

A spokeswoman for the EPA said Friday that the agency "supports the energy independence and security goals that Congress envisioned" when it created the mandate.

Still, Michael McAdams, president of the Advanced Biofuels Association, said that he hoped public opposition to the proposed changes would convince the agency to reconsider.

"Since that time, ABFA members and our many allies have clearly demonstrated that such reductions would fall disproportionately on advanced biofuels and represent a significant reversal of the Obama administration’s previous support for our industry," McAdams said.

The biofuels mandate has been an issue in two Midwestern Senate races.

In Iowa's highly competitive race, Democratic Rep. Bruce Braley supports the mandate, while his opponent, Republican Joni Ernst, said she would do away with it as along as all other energy subsidies were eliminated as well.

Democratic Sen. Al Franken, who is expected to win his re-election campaign in Minnesota, has also touted his support for the standard, arguing it's buoyed rural communities there.

The biofuels mandate was intended to develop a domestic biofuel industry as a means to reduce greenhouse gas emissions and oil imports by setting requirements for refiners to blend that fuel into conventional petroleum. Those targets accelerate annually, ending with 36 billion gallons by 2022.

Opponents say the federal blending targets are unrealistic, noting that next-generation fuels have come online too slowly. They also say there's also not enough gasoline used to safely absorb enough corn-based ethanol, which dominates the market, to meet the mark without churning out fuels with higher ethanol concentrations — known in industry parlance as the "blend wall."