WASHINGTON (AFP) - Donald Trump's Republican Party rolled out a plan on Wednesday (Sept 27) to reform America's tax code, calling for deep cuts to corporate rates and the abolition of inheritance tax in a high-stakes bid to salvage the President's agenda.

Developed in tandem with Trump's White House, the Republican plan calls for slashing the US corporate tax rate from 35 to 20 per cent - to below the 22.5 average of the industrialised world, it says.

"We're going to introduce a tax plan that's the largest tax cut essentially in the history of our country," Trump told reporters on the South Lawn of the White House, before leaving for Indiana to deliver a speech promoting the Republican plan.

"It's going to be something special," he said.

For households, the Republican plan cuts the number of tax brackets from seven to three, with a maximum rate of 35 per cent, against 39.6 at present, although the plan also mentions the "potential" for an additional top rate for the highest-income taxpayers.

"This is our best opportunity in a generation to deliver real middle-class tax relief, create jobs here at home, and fuel unprecedented economic growth," House Speaker Paul Ryan said in a statement as the plan was unveiled.

"It has been 31 years since we last got this done, and hardworking families and small businesses cannot afford to wait any longer."

The plan also seeks to encourage firms to bring back profits that have accumulated abroad by offering a one-time, low tax rate on wealth brought back from overseas.

Overhauling the tax system has long been a political Holy Grail for the Republican Party.

It was also a major Trump campaign pledge, and has taken on extra importance after his efforts to enact promised health care reform and build a border wall stalled.

But opposition Democrats savaged the reform proposal as a "perverse" system for rewarding the wealthy, and called out Trump for failing to help working and middle class American families.

"The President talked the talk. He said we're going to aim this at the middle class," Senate minority leader Chuck Schumer told reporters.

"He ain't walking the walk. This is aimed at the wealthiest people in America, they do far and away the best." .

'ECONOMIC STIMULUS'

With Republicans licking their wounds one day after their latest Obamacare repeal effort collapsed, and hours after a Trump-backed senator lost a run-off race to a hardline conservative who has threatened to upend the Washington Republican establishment, the party embraced the opportunity to roll out another top priority item.

Number two Senate Republican John Cornyn hailed it as "the best economic stimulus" possible, telling Fox News the plan would "lower the cost of living for all Americans across the board." The President and his party want to simplify the thousands-of-pages-long US tax code - to enable Americans to fill out their return on a postcard, runs the refrain.

That involves the elimination of countless loopholes and deductions.

Under the Republican plan, only two highly popular deductions are explicitly protected: for interest paid on home mortgages and for charitable contributions. Lawmakers will hammer out precisely which deductions will survive under the reform in the coming months.

Inheritance tax, or estate tax, would be scrapped altogether - a longstanding demand of Republicans who refer to it as the "Death Tax." Schumer said abolishing the estate tax would contribute to ballooning the federal deficit by awarding a US$269 billion tax break to the richest 0.02 per cent of Americans.

Ultimately the framework unveiled by Ryan "will add anywhere from US$5 trillion to US$7 trillion to our deficit," Schumer said.