UNITED NATIONS — Newly elected as president of the U.N. General Assembly, one of America’s fiercest longtime critics in Latin America is saying the dominance of a few countries has turned the United Nations into a dictatorship.

Although Miguel d’Escoto Brockmann said yesterday that his previous comments against American leaders were part of “history,” it appears that reversing decades of anti-American rhetoric will be a challenge for the former foreign minister of Nicaragua’s Sandinista government.

After his election yesterday to the presidency of the 192-member assembly, Mr. d’Escoto called the United Nations the world’s “longest-lasting dictatorship.” Members of the assembly, he said, “must unite in the struggle to democratize the United Nations” and free the world “for the sake of present and future generations … from the scourge of war among member states and acts of aggression such as those occurring in Iraq and Afghanistan.”

In a 2004 interview with the TV and radio program “Democracy Now!” Mr. d’Escoto, 75, called President Reagan “the butcher of my people.”

Hearing Reagan “talk about how we were supposedly persecuting Jews and burning down nonexistent synagogues, I was led to believe, really, that Reagan was possessed by demons,” he told the program’s host, Amy Goodman. “Frankly, I do believe Reagan, at that time, as much as Bush today, was indeed possessed by the demons of manifest destiny.”

Mr. d’Escoto, a Catholic priest, said yesterday that though he stands by his earlier statements, they are part of the past.

“People seem to want change all over,” he said. Asked whether his use of a campaign slogan favored by Senator Obama was a declaration of support for the Illinois senator’s presidential candidacy, Mr. d’Escoto — who was born in California and received his religious training in America — said: “I am not an American.”

One of Mr. d’Escoto’s biggest allies in Latin America, President Chavez of Venezuela, made an unsuccessful bid to gain a seat on the U.N. Security Council two years ago after telling the General Assembly that he could smell sulfur after Mr. Bush left the speaker’s podium. “I smell the devil,” Mr. Chavez said, to applause. But his remark turned off members of the Latin American voting bloc, who afterward refused to support his council campaign.

Diplomats said America failed in its halfhearted campaign against Nicaragua’s candidacy for the presidency of the General Assembly, which, though largely ceremonial, has become a springboard for its holders to careers as top international officials.

Mr. d’Escoto, who will assume his post September 16, “is now the president of the General Assembly and his responsibility is to bring the members together to serve the entire membership of the United Nations,” the American ambassador to the United Nations, Zalmay Khalilzad, who began his career in government as a protégé of Reagan, said yesterday.

“We certainly disagree with that characterization of the two conflicts” in Afghanistan and Iraq, Mr. Khalilzad said. But Mr. d’Escoto “is not representing his government and its sort of partisan aspects in terms of policy.” Or at least “that’s our expectation, and we have been led to believe that he understands that, and so we will wait and see,” the ambassador said.