UNITED NATIONS (Reuters) - The United States threatened on Tuesday to delay the two-year United Nations budget unless reforms are approved by the end of the year, a move that could cause havoc for U.N. operations. U.S. Ambassador John Bolton said Secretary-General Kofi Annan and his staff have acknowledged they might not have all management and other reform proposals until February, after the December 31 budget deadline. Although a U.N summit document calls on Annan to provide "recommendations to the General Assembly for decision" during the first quarter of 2006, Bolton said this was too late. "I don't think we should be in a position of losing the momentum for reform because of the budget process," he told reporters. "The reform should drive the budget process and not the other way around." Bolton said, the U.N. General Assembly, in charge of the budget, could consider a three or four-month interim budget by December 31, instead of approving the full two-year budget. "I've proposed this three- to four-month interim budget as one possible mechanism to accommodate our desire to get the reforms fully implemented in the longer-term budget," he said. Annan has estimated some $3.6 billion for the 2006-2007 regular administrative budget, a slight increase over 2004-2005. This excludes peacekeeping, which in 2005 alone amounted to $3.6 billion. Annan told reporters on Monday that member states need to approve a two-year budget by the end of this year so they knew what they had to pay and his staff could plan properly. "And if you do not do that ... you may create a serious financial crisis for the organization," he cautioned. Annan said the General Assembly could pass a supplementary budget to cover some of the reform proposals, many of which grew out of the scandal-tainted $46 billion oil-for-food humanitarian program for Iraq. But Bolton said this would not put enough pressure on the assembly to adopt the reforms being pushed by the United States, which pays 22 percent of the budget. "Business as usual has gotten us to the state where we need a revolution in reform and business as usual isn't going to accomplish that revolution," Bolton said. The European union", whose 25 members collectively pay about 40 percent of the budget, does not want a showdown next month and prefers to get as many measures passed as possible and then build flexibility into the budget for next year. The United States has only one vote in the General Assembly but budgets are usually adopted by a consensus procedure, which means Washington could block the budget as well as withhold its own dues. Bolton, his blunt remarks, also questioned the usefulness of the United Nations to the American public as the main global problem solver. "Americans are a very practical people and they don't view the U.N. through theological lenses," he said. "They look at it as a competitor in the marketplace for global problem-solving and if it's successful at solving problems they'll be inclined to use it." Many of the reforms approved at the September U.N. summit are still bogged down among the General Assembly's 191 members. They include a peacebuilding commission and a new body to replace the discredited U.N. Human Rights Commission. Among Annan's management proposals, key to the United States, are the creation of an ethics office, an oversight body, enhanced auditing and investigation and independent external evaluations.