President Bill Clinton has promised to veto the bill if it gets through the Senate but the House vote is sending shock- waves through the UN.
The bill, approved on Thursday, would slash US financial and logistical contributions to the UN. It places a ceiling of 20 per cent on the US share, compared to 31 per cent at present. Any increase would need special permission from Congress.
Also, the extra cost of Pentagon-run peace-keeping missions approved by the Security Council but not run by the UN would be deducted. The Clinton administration says this would wipe out the US contribution and - since other rich countries would probably follow suit - spell the end of all UN-run missions.
National contributions by the US and Britain - in enforcing the no-fly zone over Bosnia and the blockade in the Adriatic - greatly exceed what they pay into UN budgets.
The proposed legislation allows the costs of operations to be waived if the President certifies that the US would have acted without a UN security council resolution. But this would hardly ever be in US interests - not least since any unilateral action could be construed as illegal. Recent US operations like Somalia and Haiti have been "UN blessed", though not under UN command.
Meanwhile, American troops would be barred from serving under foreign commanders, unless a president cited a national security need. Since the end of the Cold War, the number of peace-keeping operations run by the UN has spiralled.
Of 35 undertaken since 1948, 16 are in progress. At the end of January 63,504 UN personnel from 74 countries were employed worldwide; only 947 were from the US - 883 soldiers on peace-keeping duties and 64 military observers.
The biggest operation is the UN Protection Force in Croatia and Bosnia, with nearly 40,000 troops and police, followed by 9,400 in Somalia and 5,500 in Rwanda.
The UN operation in Haiti has an authorised strength of 6,600, but only 74 are in place, as they are in the process of taking over from the US.
The US contribution is mainly behind the scenes. The US airlift which carried UN blue-helmet troops into Bosnia was bigger than the 1948 Berlin airlift. The UN operation in Rwanda was also delivered mainly by US aircraft. Although the RAF flew in the first British troops - also a "national contribution" unlikely to be recovered from the UN - most of the rest went on US aircraft. The US will recover few, if any of those costs.
Countries' contributions are assessed on the basis of their wealth and population. The US gave $318m (£200m) to the current year's peace- keeping budget, as against $132m from Japan, $90m from Germany, $79m from the Russian Federation, $77m from France and $64m from the UK, out of a total peace-keeping budget of $1bn. The regular budget and contributions are of similar size, totalling $1.1bn for the current year. The US owes $539m in back payments to the peace-keeping budget and $527m to the regular budget.