The US defense secretary, Pete Hegseth, walked into the Senate on Tuesday to defend the Trump administration’s $87.6bn supplemental funding request, facing lawmakers furious that the US-Israel war on Iran is costing far more than the White House has admitted.

Hegseth and the chair of the joint chiefs, Gen Dan Caine, faced the Senate appropriations committee, chaired by Susan Collins of Maine, as the Pentagon said it was running low on cash to keep the fight going. Of the total request, $67.1bn of the request is earmarked specifically to keep the war effort funded.

It was the pair’s first sustained public questioning since a brief ceasefire collapsed and the war roared back to life. At least two US soldiers were killed in an Iranian attack on Friday, and another died in Iraq destroying an Iranian drone, pushing the American death toll since February to 17. Nearly 100 troops have been wounded in the conflict, officials confirm, though most injuries were minor.

Patty Murray, the committee’s Democratic vice-chair, is expected to argue that the public wants the war brought to a swift, strategic close rather than tens of billions more spent to sustain it, according to a Democratic aide briefed on her remarks. Some Democrats, including Chris Coons of Delaware, plan to direct criticism at Russell Vought, director of office of management and budget, who is not testifying but who earlier told US Congress that the war’s running cost was about $30bn, a figured largely believed by experts to be a severe undercount.

Hegseth and Caine also face potential threats from within their own party. Collins and Alaska’s Lisa Murkowski, two prominent Republicans, have both crossed the aisle to back war-powers resolutions aimed at reining in the president’s authority over the conflict, and Collins has previously voiced frustration that the administration’s strategy for the war seems to shift almost daily.

House representatives have separately accused the Pentagon of stonewalling on basic figures: Betty McCollum, the top Democrat on the House defense appropriations panel, said the department has missed a deadline to detail war costs and has not disclosed how many precision munitions remain after the military burned through thousands of them in Iran.