NEW YORK/WASHINGTON (Reuters) - Democratic U.S. presidential candidate Elizabeth Warren on Friday proposed a $20.5 trillion Medicare for All plan that she said would not require raising middle-class taxes “one penny,” answering critics who had attacked her for failing to explain how she would pay for the sweeping healthcare system overhaul.

Warren said her plan would save American households $11 trillion in out-of-pocket healthcare spending over the next decade while imposing significant new taxes on corporations and the wealthy to help finance it.

“Healthcare is a human right, and we need a system that reflects our values,” Warren wrote in a 20-page essay outlining her plan. “That system is Medicare for All.”

The proposal to remake the U.S. healthcare system will face scrutiny from Warren’s more moderate Democratic opponents, who have questioned Medicare for All’s practicality.

Warren’s proposal also calls for cuts in defense spending and passing immigration reform to increase tax revenue from newly legal Americans, two steps that would face an uphill battle in Congress. The $20.5 trillion in new spending over 10 years would increase the entire federal budget by a third.

Warren, a U.S. senator from Massachusetts, is one of 17 Democrats vying for the party’s nomination to take on Republican President Donald Trump in the November 2020 election. She is near the front of the pack in opinion polls, having closed in on former Vice President Joe Biden, the early front-runner.

Medicare for All would replace private health insurance, including employer-sponsored plans, with full government-sponsored coverage, and individuals would no longer have to pay premiums, deductibles, co-pays or other out-of-pocket costs.

It would extend Medicare, the U.S. government’s health insurance program for people 65 years and older and the disabled, to cover all Americans, including the roughly 27.5 million - 8.5% of the population - who are currently uninsured.

Warren, a former law professor, has become known for a bevy of detailed policy proposals. But she had faced criticism for not detailing how she would pay for a Medicare for All plan she backs, which was introduced in the Senate by rival Democratic candidate Bernie Sanders of Vermont.

FILE PHOTO: Democratic 2020 U.S. presidential candidate and U.S. Senator Elizabeth Warren (D-MA) speaks at a campaign town hall meeting at the University of New Hampshire in Durham, New Hampshire, U.S., October 30, 2019. REUTERS/Brian Snyder/File Photo

At recent debates, Warren had refused to answer directly when asked whether she would be forced to raise middle-class taxes to cover the costs, even as Sanders acknowledged he would.

More moderate 2020 candidates such as Biden and South Bend, Indiana, Mayor Pete Buttigieg have said Medicare for All would be too disruptive and favor a more incremental approach.

‘MATHEMATICAL GYMNASTICS’

On Friday, Biden’s campaign questioned Warren’s calculations, calling them “double talk” and “mathematical gymnastics” and asserting that middle-class taxes would rise despite her vow.

“It’s impossible to pay for Medicare for All without middle-class tax increases,” said Kate Bedingfield, Biden’s deputy campaign manager. “To accomplish this sleight of hand, her proposal dramatically understates its cost, overstates its savings, inflates the revenue, and pretends that an employer payroll tax increase is something else.”

Warren, speaking to reporters in Iowa on Friday, said she was “just not sure where he (Biden) is going,” adding that her proposal and its costs were authenticated by outside experts.

“Democrats are not going to win by repeating Republican talking points and by dusting off the points of view of the giant drug companies and the giant insurance companies,” Warren said.

House of Representatives Speaker Nancy Pelosi also questioned the feasibility of enacting Medicare for All, saying in an interview with Bloomberg on Friday that Democrats should focus on expanding the Affordable Care Act, commonly known as Obamacare.

Critics like Warren note that the current U.S. healthcare system - a patchwork of private insurance often provided by employers or obtained through Obamacare marketplaces and public programs covering the poor, elderly and disabled - is the most costly in the world despite leaving tens of millions uncovered.

Medicare for All legislation stands little chance of passing Congress, where Democrats control the House and Republicans control the Senate.

The plan relies on aggressive ways of lowering healthcare costs, including major cuts in prescription drug prices and significant reductions in administrative costs by eliminating private insurers.

“She makes some assumptions about how effectively healthcare costs could be contained that may not pan out,” said Larry Levitt, a health policy expert at the Kaiser Family Foundation.

Employers would be asked to repurpose the money they currently spend on workers’ healthcare into Medicare contributions, while billionaires, high-earning investors and corporations would face trillions of dollars in higher taxes.

In an effort to appease union leaders, some of whom have expressed skepticism about giving up hard-fought healthcare plans, Warren said employers that already offer benefits under a collective bargaining agreement could reduce their contributions if they pass the savings along to workers.

Warren released two letters supporting her calculations from several experts, including Simon Johnson, the former chief economist for the International Monetary Fund; Donald Berwick, who oversaw Medicare in the Obama administration; and Mark Zandi, the chief economist at Moody’s Analytics.

An online calculator launched by Warren’s campaign showed an average family of four with employer-provided insurance would save $12,378 per year.

Warren said with her Medicare for All plan in place, projected total healthcare costs in the United States over 10 years would be just under $52 trillion - slightly less than maintaining the current system.