(Adds comments from governor, White House, background, senator blocking nominations)
WASHINGTON, Oct 18 (Reuters) - Iowa Governor Kim Reynolds said U.S. President Donald Trump had told her he was committed to biofuels, at a time when the administration is eyeing changes to the quantities it demands suppliers use.
U.S. law requires fuel companies to add biofuels like ethanol to the nation's fuel supply through the 'renewable fuel standard', adopted in 2005. The Trump administration is considering lowering the mandatory level, a worry for corn-growing states like Iowa.
Reynolds said she held separate calls with Trump and the U.S. environmental regulator on Wednesday, in which she urged the Trump administration not to make those changes.
"Both of them personally committed to me their continued commitment to the renewable fuel standard," Reynolds said, adding that the call with Trump was "positive."
However, White House spokeswoman Sarah Sanders said the administration "didn't make any assurances" on renewable fuel standard (RFS) levels.
"No definitive decision was made on RFS", she said.
The biofuels industry has been ratcheting up pressure in Washington in response to actions from the Environmental Protection Agency (EPA) it sees as threatening the more than decade-old program, designed to boost use of ethanol and other renewables and reduce carbon emissions.
Independent oil refiners have pushed the Trump administration to soften requirements for ethanol use, which costs them hundreds of millions of dollars annually.
On Tuesday, EPA chief Scott Pruitt met with senators to discuss the issue. In a statement after the meeting, Iowa Republican Senator Joni Ernst said she had expressed "significant concerns" over the agency's recent moves to potentially set biodiesel requirements for 2018 and 2019 at "substantially lower volumes."
Senator Charles Grassley, an Iowa Republican, said he told Pruitt during the hour-long meeting "that supporting biofuels isn't just good policy. It's also what President Trump promised."
EPA spokeswoman Liz Bowman said that Pruitt would not want "to take any steps to undermine the objectives in the statute of the RFS."
Reynolds said she would meet next week with Vice President Mike Pence and Pruitt in Washington and urged Iowans to contact lawmakers and administration officials to "help them feel the pressure - and they are."
Last month, the EPA said it was looking to cut 2018 biodiesel blending requirements, roiling markets and drawing criticism from the country's farm belt. In July, it proposed cutting total volumes of all renewable fuels use for next year.
A group of 33 senators wrote to Trump this week urging the EPA to maintain levels for 2018 and increase its proposed 2019 biodiesel requirements.
Late on Tuesday, the Senate Committee on Environment and Public Works postponed a planned hearing for Wednesday to consider the nominations of four EPA officials. Senator Tammy Duckworth, an Illinois Democrat, said she was placing a hold on two EPA nominees over the ethanol issue.
Ernst said in a statement on Wednesday she was declining to support one of the nominees over concerns about the EPA's treatment of RFS.
(Reporting by David Shepardson and Emily Flitter; Editing by Chizu Nomiyama and Rosalba O'Brien)