The Republican tax plan would deliver major gains for the richest 1 percent of Americans and uneven benefits for the middle class, an analysis by a leading group of nonpartisan experts found Friday, creating a fresh hurdle for Congress as it pivots toward writing legislation overhauling the tax code.

The analysis by the Urban-Brookings Tax Policy Center found that most of the cuts would benefit people making more than $730,000, with average tax savings of $129,000 once the plan goes into effect. Over time the benefits to the wealthy would grow, with 80 percent of the cuts in 2027 going to households making more than $900,000, with their taxes dropping by more than $200,000 on average.

Most other households would see more-modest gains — challenging President Trump's repeated assurances that the plan will benefit the middle class, not the rich, and complicating Republicans' legislative agenda.

[Wonkblog: The GOP tax plan, explained in simplest possible terms]

Next year, a household earning between about $48,000 and $86,000 would save $660 on its taxes. But roughly 1 in 7 households in this group could end up paying more in taxes next year — a proportion that would nearly double over the next decade. Among households earning between $150,000 and $217,000, a third would start paying more as soon as the plan went into effect.

"We will cut taxes for everyday, hard-working Americans, and we're going to cut them substantially," Trump said Friday in a speech to the National Association of Manufacturers in Washington. "Our framework ensures that the benefits of tax reform go to the middle class, not the highest earners."

Trump's remarks came as Senate Republicans prepared to set aside their quest to repeal the Affordable Care Act and turn to a sweeping tax overhaul.

Senate Republicans released a budget document Friday that is a key precursor for any tax bill, setting out procedures that will allow the legislation to pass with a 51-vote majority rather than the usual 60-vote supermajority. The Senate Finance Committee and House Ways and Means Committee will have until Nov. 13 to draft tax bills that cost no more than $1.5 trillion in lost revenue.

The draft budget resolution is set to be passed through the Senate Budget Committee next week, setting up floor action early next month.

After months of intraparty battles that pitted conservative hard-liners against House leaders and moderates, the tax framework generated enthusiasm this week across the GOP's usual ideological fault lines.

But new divides promise to emerge along more parochial lines as members take sides based on constituents' wallets rather than philosophy.

[It was candidate Trump’s best trick. Now it’s stalling President Trump’s agenda.]

None was more immediately divisive than the proposal to eliminate individuals' ability to deduct state and local taxes from their income subject to federal tax — a proposal that could offset more than a trillion dollars of revenue losses over 10 years. That generated immediate pushback from lawmakers in high-tax states where, in some cases, half of taxpayers claim that deduction.

At least three GOP House members from New York and New Jersey issued statements of concern about the plan to roll back the state-and-local-tax deduction. Other members worried whether the framework, which would eliminate personal exemptions and many itemized deductions, would raise taxes for high-middle-income earners.

"It's not fair to give the entire country a tax break on the backs of the citizens of these six or seven states," said Rep. Tom MacArthur (R-N.J.), who called himself a "loud objector" to the framework but not yet an opponent. "I've made it crystal clear at every possible setting that I can."

Several key lawmakers, including Senate Finance Committee Chairman Orrin G. Hatch (R-Utah), have expressed a willingness to maintain the deduction, but arithmetic could be hard for tax writers to ignore. Rep. Tom Reed (R-N.Y.), a House Ways and Means Committee member, suggested this week the deduction could be converted to a less costly credit that could be better targeted to middle-class families.

A fight over the state-and-local-tax deduction is the largest of dozens of small battles that could ensue over the tax incentives that litter the existing code and must be stripped out if lawmakers hope to pass an aggregate $5 trillion rate reduction under a budget allowing for only $1.5 trillion in lost revenue.

Congressional tax writers said they were confident the promise of increased economic growth and lower overall rates would keep Republicans united as the committees start hacking away at various provisions.

"There's always going to be that question about, 'Well, I had this before and I don't have it now,' " said Rep. Mike Kelly (R-Pa.), also a Ways and Means member. "We keep falling back to the same thing: We are significantly lowering rates. Would it be nice to maintain all these other things that people like? Yeah, but you can't do it and still maintain some kind of revenue stability."

Business provisions could be thorny, opening divides between manufacturers and service-oriented enterprises, between large corporations and smaller firms, and between companies that rely on borrowing to grow and those that tend to raise equity.

Larger concerns also threaten to derail the effort, including the need to combat the perception that the plan is tilted toward the rich. Several Republicans lamented the optics of the GOP plan raising the bottom bracket from 10 percent to 12 percent and lowering the top bracket from 39.6 percent to 35 percent.

Rep. Charlie Dent (R-Pa.) called the bottom rate going up and top rate going down "an optical snafu" and said, "That issue's going to have to be addressed."

The plan does leave open the potential that a higher bracket could be added, and key lawmakers urged their fellow Republicans to withhold final judgment until the tax-writing committees crafted a final product.

"We now have a basic framework that works, and there are going to be a lot of minor issues that we're going to want to debate," said Rep. James B. Renacci (R-Ohio), a Ways and Means member. "But at the end I would ask everyone to look at what their net tax effect is after we reduce the rates. . . . I'm hoping we look at it from the position of what's best for the country."

The Tax Policy Center analysis relied on a number of assumptions, using past proposals to fill in details missing from the new plan. Outside experts said that puts real limits on interpreting the results — and Republicans said the findings were biased.

The analysis said the mixed results for middle-income earners were because of the loss of itemized deductions, particularly the ability to deduct state and local property taxes from income.

The loss of the personal exemption, which shields $4,050 of income from federal taxes for every household member, also would play a major role in increasing taxes for some households, the analysis found — an effect that would get worse over time because the amount of the personal exemption kept pace with inflation.

The analysis also found the plan would provide disproportionately large benefits for businesses compared with what the middle class and low-income Americans would receive.

"A major feature is tax collections would shift dramatically, from businesses to individuals," said Eric Toder, a co-director of the Tax Policy Center.

The tax plan would increase the deficit by $2.4 trillion over the first decade, the center found.

A spokeswoman for Senate Majority Leader Mitch McConnell (R-Ky.) dismissed the findings. "This analysis is based on guesswork and biased assumptions designed to promote the authors' point of view rather actual detail from a bill that has not yet been written by the committees," Antonia Ferrier said.

Ways and Means Committee Chairman Kevin Brady (R-Tex.) said the analysis was biased and had failed to factor in the blueprint's provision to create an additional top rate bracket for the highest-income taxpayers.

"Republicans are unified in delivering tax reform that will lower taxes on middle-class Americans, ensure they are able to keep more of their hard-earned money, and grow our economy," Brady said in a statement. "We will deliver on this promise and our bill will improve the lives of all Americans."

Damian Paletta contributed to this report.