Thousands of protesters swarmed Columbia University on Monday while Iranian President Mahmoud Ahmadinejad gave a major address to students there.

Ahmadinejad defended his country and his beliefs at the heavily attended speech, which was also broadcast on Iranian state television. The university came under fire over the past several days for its decision to host a leader whose country the White House has accused of sponsoring terrorism.

Ahmadinejad’s address was perhaps the most significant speech by a foreign leader at an American university since Chinese President Hu Jintao spoke at Yale in April 2006. As Hu spoke, more than 1,000 demonstrators protested around Yale’s campus decrying China’s record of human rights. The scene at Columbia on Monday was even more chaotic, students said.

In his afternoon address at Columbia’s World Leaders Forum, Ahmadinejad defended his right to question the Holocaust, raised doubts over whether al-Qaida was truly behind the Sept. 11 terrorist attacks, and asserted that the “phenomenon” of homosexuality does not exist in Iran.

Ahmadinejad also responded to pointed questions regarding Iran’s human rights record and its foreign policy.

In the days leading up to the event, Columbia President Lee C. Bollinger received his own share of angry questions for allowing Ahmadinejad to speak at the university, though he challenged the leader in his introduction on Monday.

“Mr. President, you exhibit all the signs of a petty and cruel dictator,” Bollinger said, drawing loud applause.

Protesters agreed. Thousands gathered around campus at Columbia and along two blocks across from the United Nations, where the U.N. General Assembly opened its session today.

Ahmadinejad was in the United States for that session and was asked to speak at a World Leaders forum.

He faced a colder reception at other sites around the city. Last week, the New York Police Department rejected the Iranian leader’s request to visit Ground Zero. And last year, Columbia officials retracted their invitation for Ahmadinejad to speak at the same forum, citing security and logistical concerns.

Columbia officials said the Iranian leader recently contacted a Columbia history professor and, speaking through Iran’s ambassador to the United Nations, expressed interest in speaking at the university. The speech on Monday was Ahmadinejad’s first-ever address at an American university, though he has been to the United States before.

In his speech, Ahmadinejad attempted to portray himself as an intellectual and not a radical ideologue. His government, he said, is one that respects reason and science. He often quoted from the Koran and criticized the United States on a number of issues, from the atomic bombings of Hiroshima and Nagasaki during World War II to the Bush administration’s warrantless wiretapping program.

At another moment, Ahmadinejad accused Israel of using the Holocaust as a justification for mistreating Palestinian citizens.

“Why is it that the Palestinian people are paying the price for an event they had nothing to do with?” Ahmadinejad asked.

Women in Iran, the president said, have great freedoms. And the country’s nuclear program is entirely peaceful and entirely within the country’s rights, despite attempts by “monopolistic,” “selfish” powers to stop it from doing so, he said, adding, “How come is it that you have that right, and we can’t have it?”

In phone interviews on Monday night, Columbia students said campus was chaotic during the speech, with the increased presence of security officials and members of the media, along with protesters hoisting signs around campus. Dasha Wise, a freshman at Columbia, said she supported Ahmadinejad’s right to visit to the University, though she said it had sparked controversy on campus.

“I think that Ahmadinejad should have been able to speak here because it provides a different perspective so that people can understand his point of view,” she said.

Classmate Miguel Castro, who attended the speech, said he also supported Ahmadinejed’s right to speak. The audience was receptive to the President’s visit, Castro said.

“The audience members were very mature, and they acknowledged his points and would clap during several good arguments,” he said, including once when he bemoaned the plight of the Palestinians.

Politicians, meanwhile, lambasted Bollinger and Columbia for hosting the Iranian leader.

“A man who is directing the maiming and killing of Americans troops should not be given an invitation to speak at an American university,” said Sen. John McCain, R-Ariz. and a presidential candidate, referencing Iran’s alleged support of Iraqi insurgents. Columbia, he said, should not be “rolling out the red carpet for the leader of a terrorist-sponsoring regime.”

New York Sen. Hillary Clinton, a Democratic presidential candidate herself, said that had she been in Bollinger’s place, Ahmadinejad would not have been invited to speak. Former Tennessee Sen. Fred Thompson, a GOP candidate, went one step further: He said he would not have allowed Ahmadinejad in the United States, period.

But Bollinger defended the event, saying the speech “intended to further Columbia’s long-standing tradition of serving as a major forum for robust debate, especially on global issues,” according to a statement posted to Columbia’s Web site.

“We must respect and defend the rights of our schools, our deans and our faculty to create programming for academic purposes,” he said. “Necessarily, on occasion this will bring us into contact with beliefs many, most or even all of us will find offensive and even odious. We trust our community, including our students, to be fully capable of dealing with these occasions, through the powers of dialogue and reason.”

—The Associated Press contributed reporting.