Posted: APRIL 24, 2017

WASHINGTON — President Trump has instructed his advisers to make cutting the corporate tax rate to 15 percent a centerpiece of his tax-cut blueprint to be unveiled this week, according to people with knowledge of his plans, even if that means a significant reduction in revenue that could jettison his campaign promise to curb deficits.

Cutting the corporate tax rate to 15 percent from its current 35 percent level was one of Mr. Trump’s marquee campaign promises, part of his vision of carrying out “maybe the biggest tax cut we’ve ever had.” But he has yet to publicly embrace the move since taking office, and his decision to do so now could set up a showdown with Congress over a proposal that would most likely blow up the deficit.

The White House is planning to formally roll out its tax plan on Wednesday, ending months of speculation about the president’s intentions for rewriting the tax code and following a prolonged period of confusion in which he and his top advisers sent mixed messages about what elements they favored and how the tax cut would be structured. The people who described Mr. Trump’s corporate tax cut target, first reported by The Wall Street Journal on Monday, did so on the condition of anonymity because they were not authorized to discuss it before an official announcement.

The president plans to unveil the tax cut during a week when Republicans will be trying to pass a spending measure needed to keep the government from shutting down. Repealing and replacing the Affordable Care Act remains a legislative priority, although whether it is considered more important than a tax overhaul changes frequently.

The 15 percent rate is lower than what House Republicans proposed in the tax cut blueprint being pitched by Speaker Paul D. Ryan, and it could be difficult to move through Congress. Senator Orrin G. Hatch of Utah, the Republican chairman of the Senate Finance Committee, said on Monday that such a deep cut might not be well received by Mr. Trump’s party because of its potential to increase the deficit.

Mr. Mnuchin also said the Trump administration would lay out plans to cut middle income tax rates, simplify the tax code and make American companies more competitive with foreign ones.

The White House would not say if it is on board with the “border adjustment” tax, a 20 percent tax on imports that is central to Mr. Ryan’s plan. There are also lingering questions about what shape the rest of the plan will take, and even about the timetable for pushing it through. Mr. Trump has said that he still believes a health care overhaul effort that collapsed last month must be completed before the plan to rewrite the tax code can advance.

White House officials declined to comment on the 15 percent target, which people close to the administration cautioned could change between now and the announcement on Wednesday, perhaps repeatedly. They warned that the details were sketchy at best, and others who have discussed the tax overhaul plan with administration officials in recent days said there was still indecision at the highest levels about what elements to include and in what form.

The Wednesday deadline, set hastily by Mr. Trump last week in a comment that appeared to catch some of his closest advisers off guard, was an effort to showcase an ambitious plan for economic growth during his first 100 days in office. During the campaign, he promised to introduce a tax cut proposal to Congress in the first 100 days. But he has had no major legislative achievements to point to as evidence of an activist economic agenda.

The 15 percent cut represents a return for Mr. Trump to the economic vision that animated his campaign, and a victory of sorts for Mr. Mnuchin, who has been a supporter of the plan. The cut also helps Mr. Mnuchin jockey for position as the driving force behind the tax overhaul effort.

“Our analysis has always shown that of all the economic bang for the buck from all of the changes that were in the original Trump plan, you get the most economic juice from cutting the corporate rate,” said Stephen Moore, an economist at the Heritage Foundation who advised Mr. Trump’s presidential campaign.

One question that Mr. Trump will have to answer, Mr. Moore said, is whether the 15 percent rate would apply only to corporations or to small businesses, as well. But there are plenty of other unknowns, he added.

“They can change their minds,” Mr. Moore said. “They’ve been all over the map.”

Members of Mr. Trump’s team of economic advisers are set to meet with Republican leaders in Congress on Tuesday to discuss the plan.

Mr. Hatch said in an interview with NBC that such a deep cut was troublesome because it would add to the deficit. “I have some real reservations about it, but I’m open to good ideas wherever they come,” Mr. Hatch said. “All I can say is, I think it’s got a long way to go and it’s going to be a difficult matter to get through both bodies.”

Roberton Williams, a fellow at the Tax Policy Center who analyzed Mr. Trump’s campaign tax plan, said its high cost would make it more difficult to push through Congress.

“It’s very expensive, and that’s a problem,” Mr. Williams said. “It’s a real heavy lift to get the revenue necessary to pay for these things.”

Mr. Williams said the president’s recent emphasis on tax “cuts” suggested that he was prepared to lose revenue and hope that economic growth will make up the difference. However, Mr. Williams said, such a plan could be difficult for fiscal conservatives to swallow.

“That makes it a lot harder with the budget hawks in Congress,” he said.

Republicans are expecting to pass tax legislation without the support of any Democrats using the Senate’s budget reconciliation procedure. That requires only 51 votes for passage. But if changes to the tax code add to the deficit, they would expire after 10 years, adding uncertainty for businesses and possibly hurting economic growth.

Economic advisers from Mr. Trump’s campaign had been unhappy that he seemed to be drifting away from the tax principles that helped get him elected. But on Monday, Lawrence A. Kudlow, one of the economists who helped craft Mr. Trump’s plan, said he was pleased that Mr. Trump appeared to be returning to those roots.

“We were at 15 percent from Day 1,” Mr. Kudlow said, lamenting that Mr. Trump’s new economic advisers had discussed scrapping the campaign tax plan. “All the noise in the last week or 10 days sounds like they haven’t junked the plan.”