President Donald Trump reportedly will make the announcement during a campaign trip to Council Bluffs, Iowa on behalf of Republican congressional candidates.
The president's move has long been sought by corn growers in the American Midwest, because it would significantly expand the market for their crops.
It is opposed by representatives of the oil and gas industry, who see ethanol as unnecessary competition, and scientists who contend that burning ethanol on hot days increases ground-level ozone pollution and smog.
Trump's planned announcement is seen as something of a reward for Iowa's longtime Republican senator, Chuck Grassley, who as Senate Judiciary Committee chairman oversaw the successful fight to confirm U.S. Circuit Judge Brett Kavanaugh to the Supreme Court.
Grassley has been a loud and persistent advocate for ethanol and his farmer constituents, and crossed swords with the administration earlier this year when it appeared it was going to roll back the allowable amount of ethanol used in fuel blends.
In a tweet, Iowa's other senator, Joni Ernst, thanked the president "for maintaining your commitment to Iowa's farmers."
The U.S. Environmental Protection Agency is now expected to publish a new rule in the Federal Register this week that will allow high-ethanol blends as part of a package of proposed changes to the ethanol mandate.
The change would allow year-round sales of gasoline blends with up to 15 percent ethanol. Gasoline typically contains 10 percent ethanol.
The EPA currently bans the high-ethanol blend, called E15, during the summer because of concerns that it worsens smog on hot days. As a result, the current rules prevent retailers in much of the country from offering E15 from June 1 to Sept. 15.
Proponents of the ethanol industry have long refuted this claim.
The new rule would allow E15 sales during the summer months beginning in 2019.
