The Energy Department frowned on relaxing federal requirements to boost the use of ethanol in gasoline.

Any reduction in the renewable fuel standard would sap investment in biofuel technology and undermine efforts to wean the nation off oil and reduce greenhouse gases, Deputy Assistant Energy Secretary Steven Chalk said Thursday.

"Keeping that in place is very important to us," Chalk told the Senate Environment clean air subcommittee.

Chalk made the comments as the Bush administration is considering a request by Texas Gov. Rick Perry to halve the ethanol requirement this year, from nine billion gallons to 4.5 billion gallons, because of high corn prices.

The renewable fuel standard was expanded in last year's energy bill to require 36 billion gallons of biofuels to be blended into gasoline by 2022.

In April, Perry, a Republican, asked EPA for a waiver, saying the ethanol requirements were having an "unnecessarily negative impact" on Texas' livestock industry, which relies on corn and soybeans to feed its cattle.

Perry met in Washington Wednesday with EPA Administrator Stephen Johnson, who will ultimately decide whether a waiver is granted. More than four dozen House Republicans and two dozen GOP senators, including presidential candidate John McCain, have written EPA in support of a waiver.

And they are joined by some rare allies -- environmentalists.

The Clean Air Task Force, the Environmental Working Group and Friends of the Earth, in a joint statement Thursday, said the ethanol mandate should be suspended, albeit for different reasons.

"The petition to waive the mandate provides EPA with a much-needed off-ramp ... to examine the ways in which biofuels threaten climate, water quality and biodiversity," said Jonathan Lewis, an attorney with the Clean Air Task Force.