UNITED NATIONS (Reuters) - Argentina's brash libertarian President Javier Milei, speaking at the United Nations General Assembly, criticized the organization as a "Leviathan" monster, rejected its 'Pact for the Future' and pledged instead an "agenda of freedom."

In a fiery speech where he also said the UN had become "powerless" in its key role to help prevent conflicts, Milei attacked the body's future pact adopted on Sunday calling it "socialist" and said the UN's remit had become "distorted".

"It has become a multi-tentacled Leviathan that seeks to decide what each nation state should do and how the citizens of the world should live," the right-wing economist and former pundit said, a reference to the giant mythological sea serpent.

"The same always happens with the ideas of the left. They design a model according to what human beings should do, and when things turn out differently, they repress, restrict and curtail their freedom."

Milei, who clashes regularly with political opponents, is battling to restore economic stability in Argentina after years of crises, with tough austerity measures that are helping to turn around a deep fiscal deficit, but aggravating a recession.

Before he decided to run for president, the former TV "shock jock" commentator even attacked Pope Francis, calling him a "son-of-a-bitch preaching communism". The two, however, have sought to mend ties since Milei took office in December.

(Reporting by Nicolas Misculin and Lucila Sigal in Buenos Aires; Writing by Adam Jourdan)