WASHINGTON (Reuters) - U.S. Treasury Secretary Steve Mnuchin said the plan for "the biggest tax cut" in U.S. history due to be released later on Wednesday by the White House would cut the business tax rate to 15 percent, including for small businesses.

"This is going to be the biggest tax cut and the largest tax reform in the history of our country," Mnuchin said at a news forum in Washington. He said there was fundamental agreement between President Donald Trump's administration and the Congress on the goals of the tax reform, and the details would be worked out.

Separately, House of Representatives Speaker Paul Ryan said he had seen a "sneak preview" of the plan. "We like it a lot, it puts us on the same page, we’re in agreement on 80 percent and on the 20 percent we’re in the same ballpark," Ryan said.

(Reporting by Amanda Becker and Ginger Gibson; Writing by Washington Newsroom)