Washington DC - Republicans vowed Wednesday to tackle the "stunning" US national debt, as lawmakers began work on President Donald Trump's plan for the most radical downsizing of the federal government in decades.

The House Delivering on Government Efficiency subcommittee will be the legislative arm of tech billionaire Elon Musk's efforts as Trump's right-hand man to save $1 trillion by attacking fraud and waste.

Its first hearing – "The War on Waste: Stamping Out the Scourge of Improper Payments and Fraud" – featured testimony from a former FBI agent and the head of a welfare fraud watchdog.

"This committee will be laser-focused on bringing full transparency to waste, fraud, and abuse within the federal government and presenting the plans to fix the tremendous problems we expose," chair Marjorie Taylor Greene said in her opening statement.

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"We, as a country, are $36 trillion in debt. That is such a stunning amount of money. It's absolutely staggering to even comprehend how we as a people, we as a country, found ourselves here."

The hearing was convened with government workers staging demonstrations against deep staffing cuts ordered by Musk and his Department of Government Efficiency (DOGE).

Critics say the world's richest man has enormous conflicts of interest as a major government contractor, although Trump – without producing any evidence – claims that his "efficiency czar" has already uncovered tens of billions of dollars in fraud.

Republicans have largely backed the DOGE agenda, although funding cuts at the National Institutes of Health have been met with mild dissent.

A prominent voice on the party's hard right with a history of bigoted comments, Greene has been brought from the fringes into the center of Republican politics as Trump's influence has grown.

The Georgia lawmaker, who was barred from serving on committees in her first two years in office, posted on X ahead of the hearing that "God is washing away bad things and our country is beginning to heal."

Musk, newly emboldened by a Trump executive order giving him a veto over government hiring and firing, told reporters in the White House on Tuesday that DOGE's work was "maximally transparent."

But Democrats, initially open to the concept of DOGE, have soured on Musk over his efforts to dismantle federal agencies, which they say are shrouded in secrecy.

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"I have zero interest working with... the House Republicans on this committee, to help them with anything as it relates to DOGE," House Democrat Robert Garcia of California told MSNBC.

"What we are there for, and what we're there to do, is to fight – to push back on the lies to bring attention to what's going on right now at our agencies."

Trump and Musk are facing multiple legal challenges, however, as they try to lift emergency orders blocking the dismantling of federal agencies, holds on grants, and the firing of government watchdogs.

The White House lost an appeal in Boston on Tuesday upholding a decision to block Trump's freeze on federal grants and loans.

On the same day, Trump fired an inspector general overseeing USAID, after he filed a report warning that the foreign aid freeze could leave the humanitarian agency at risk of misusing funds.

As with all his firings of inspectors general, the move looks on its face to be illegal as Congress is supposed to be given 30 days' notice.