SPRINGFIELD, Mo. — President Trump on Wednesday pitched a sweeping tax overhaul that he said would unleash the American economy and help ordinary people, promising that a large corporate tax cut and trims to individual income tax rates would boost the middle class.

The president wrapped his message in the populist rhetoric that powered his presidential campaign. But he described a plan that on its surface appears to offer relatively little to ordinary Americans, granting instead huge tax cuts — “the biggest ever,” he said — to corporations and their shareholders.

Mr. Trump gave few specifics on Wednesday beyond a goal of slashing the corporate tax rate to 15 percent, down from 35 percent, and eliminating “loopholes and complexity that primarily benefit the wealthiest Americans and special interests,” a reference to his call to scrap some itemized deductions in the code.

The politically difficult legislation has yet to be drafted despite months of private negotiations among members of the Trump administration and Republicans on Capitol Hill. Time is running out for enactment of the bill before year’s end, and the White House is keenly aware that if Mr. Trump fails to deliver his promised tax cuts, he will emerge from his first year in office devoid of any major legislative accomplishments.