 UNITED NATIONS (Reuters) - Nine former U.S. ambassadors to the United Nations warned Congress in a letter on Tuesday that slashing funding for the world body would weaken Washington’s global influence by ceding “the agenda to countries that can be hostile to our interests.”  The ambassadors - Andrew Young, Donald McHenry, Thomas Pickering, Edward Perkins, Madeleine Albright, Bill Richardson, John Negroponte, Susan Rice and Samantha Power - served under both Republican and Democratic presidents.  MORE FROM REUTERS Trump's concession on wall funding removes obstacle from spending talks State prosecutors urge Trump not to withdraw from Paris accord “Cutting funding to the U.N. ... will only damage U.S. national security and our position in the world,” Albright told reporters. “Other powers, most prominently China and Russia, will do everything they can to fill the leadership gap.”  The letter urged Congress to avoid drastically cutting U.N. funding and to give current U.S. Ambassador Nikki Haley and U.N. Secretary-General Antonio Guterres time and space to reform the world body to make it more efficient, effective and responsive.  The United States is the biggest U.N. contributor, paying 22 percent of the $5.4 billion core budget and 28.5 percent of the $7.9 billion peacekeeping budget. These assessed contributions are agreed by the 193-member U.N. General Assembly.  Trump said the U.S. share of those budgets was “unfair” and has proposed an unspecified reduction in funding for the United Nations and its agencies, as well as enforcement of a 25 percent cap on U.S. funding for peacekeeping operations.  Some U.N diplomats have also voiced concern about who could fill a U.S. cash void.  “There is an argument to be made about the U.S. inadvertently creating a ‘China first’ policy, rather than ‘U.S. first’ policy if they walk away and leave space,” said a senior U.N. diplomat, speaking on condition of anonymity.  Trump told U.N. Security Council ambassadors on Monday - over lunch at the White House - that if the world body reforms how it operates, then the U.S. investment would be worth it.  “If we do a great job, I care much less about the budget because you’re talking about peanuts compared to the important work you’re doing,” Trump told the 15 council envoys.  U.N. Secretary-General Guterres met briefly with Trump at the White House on Friday for the first time since both took office earlier this year.  The State Department said this month it was ending funding for the U.N. Population Fund (UNFPA), the U.N. agency focused on family planning as well as maternal and child health in more than 150 countries. Guterres warned that the cut could have “devastating effects.”  