NEW YORK, (Reuters) - United Nations chief Antonio Guterres said on Tuesday he is trying to convince U.S. President Donald Trump's administration of the value of investing in foreign aid and diplomacy and warned that if Washington pulled back as a global leader, other states would step up.

Trump has proposed cutting U.S. diplomacy and aid budgets by about a third, or nearly $19 billion. This includes cutting some $1 billion from U.N. peacekeeping funding and a steep cut to funding for international organizations.

"We are doing our best in dialogue with the administration and Congress to make the U.S. understand that funding development aid, funding foreign policy in general, funding organizations like the U.N., is also in the interests of the American people," Guterres told an event at New York University.

Congress sets the federal government budget, and Republicans who control both houses and Democrats have said they do not support such drastic cuts.

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.

Guterres also said if a power like the United States pulled back from a global leadership role, others could fill the void.

"It's not only the Russias and the Chinas that are occupying the ground; if you look at Saudi Arabia, Turkey, Iran, the regional powers in many parts of the world - when the big powers leave some space they will occupy it," he said.

"Sometimes this then has consequences and especially when everything is linked," Guterres said. "If you leave a void to others to occupy you might be creating a problem (for) your own internal security."