The issue could present problems for Speaker Paul D. Ryan as he makes the case for a tax overhaul at a factory in Ohio on Wednesday. The House Ways and Means Committee will not hold hearings until later this month to turn Mr. Trump’s tax-reform wish list into an actual bill, but Republicans have promised it will be made law by the end of the year.

The administration is still tinkering with how best to translate its sparse initial wording into legislative language. When the proposal was first presented, government officials were not yet ready to articulate, for instance, how a small business would be defined under the new tax plan.

The lack of answers on such fundamental issues leads only to more questions. Officials were also still debating the future of the so-called carried interest tax loophole, under which executives of private equity companies currently pay taxes on their compensation at a relatively low rate of about 24 percent.

The pass-through issue is another area of disagreement between the White House and House Republicans, who proposed a higher top pass-through tax rate of 25 percent in “A Better Way,” the legislative blueprint they issued last summer. Proponents of the higher rate argue that it could prove critical for helping Republicans pass tax legislation that does not cause deficits to balloon and that it would reduce incentives for individuals to try to game the system by incorporating themselves.

Stephen Moore, a Heritage Foundation economist who advised Mr. Trump during his campaign and talks frequently with administration officials, said Mr. Trump’s economic team knew it was problematic to have employers paying lower tax rates than their workers because of low pass-through rates. He said the White House was inclined to tax income that is reinvested in businesses at a lower rate than money that is pulled out and used for personal reasons.

“We don’t want the owners to just take the money out of the company and use it for personal consumption, even though they have every right to do that,” Mr. Moore said. “The goal is to get more businesses reinvesting in their companies.”