A tenured professor at the University of Chicago last night blamed the “Israel Lobby” in America for both the Iraq war and the attacks of September 11, 2001.

Speaking to a crowd of hundreds at the Cooper Union, he was met mostly with support from two other professors, Tony Judt of New York University and Rashid Khalidi of Columbia.

“The Israel lobby was one of the principal driving forces behind the Iraq War, and in its absence we probably would not have had a war,” said the University of Chicago professor, John Mearsheimer, at a forum organized by the London Review of Books.

Later, in response to a question from the audience, Mr. Mearsheimer claimed that the “animus to the United States” of Qaeda terrorist mastermind Khalid Sheik Mohammed “stemmed from U.S. foreign policy toward Israel.”

This, Mr. Mearsheimer asserted, “Simply can’t be discussed in the mainstream media.” He appeared to have forgotten the article that ran on September 20, 2001, on the op-ed page of the largest circulation American newspaper, The Wall Street Journal, that began with the sentence: “Is American support of Israel behind the hatred of this country that pervades the Arab world and that literally exploded into the World Trade Center and the Pentagon on Sept. 11?”

In fact, Mr. Mearsheimer claimed, “There is a considerable amount of evidence that there is a linkage between the two” — the two being American support for Israel and the terrorist attacks of September 11.

The event last night at Cooper Union was a discussion of a paper issued by the Kennedy School of Government at Harvard University earlier this year and published in an edited version in the London Review of Books. The paper was authored by Mr. Mearsheimer and by an academic dean and professor at the Kennedy School, Stephen Walt. It described what it alleged to be a vast Israel lobby that included the editors of the New York Times, “neoconservative gentiles,” the Brookings Institution, and students at Columbia. The “Lobby,” the paper said, had the “ability to manipulate the American political system,” “a stranglehold on the U.S. Congress,” and was actively “manipulating the media.”

The Kennedy School quickly distanced itself from the paper, removing its logo and printing a large disclaimer on the front cover of the paper.

A Brookings scholar and former American ambassador to Israel, Martin Indyk, said at the Cooper Union debate that the paper “lowers itself to the level of anti-Semitism” and was “very sloppy” in its scholarship.

A former foreign minister of Israel, Shlomo Ben-Ami, said at the event that the term “Lobby” as used in the paper “is a cover for the Jews, basically,” and that there was an “element of scapegoating” in the case made by Messrs. Mearsheimer and Walt.

Messrs. Khalidi and Judt both bemoaned the fact that America’s relations with Israel were not debated more hotly and frequently.

“In American political discourse there is one side to this debate,” Mr. Khalidi said. “There are not two sides to this debate.”

Mr. Judt said that the New York Times asked him whether he was Jewish before publishing his opinion piece on the Walt-Mearsheimer paper. Mr. Judt said he is Jewish, but he sought to distinguish himself from the American Jewish community. “For many American Jews, there is no daylight between America’s interests and Israel’s interests, the two are one and the same. We have to somehow unravel this connection,” he said. He tried to draw a distinction between anti-Zionism and anti-Semitism.

Mr. Indyk criticized the Iran-Libya Sanctions Act signed by President Clinton as “counterproductive.” He said it had split America from its allies in Europe. The bill had been championed by the American Israel Public Affairs Committee. Mr. Indyk also noted he had been criticized by pro-Israel groups in America while serving in the State Department. “I have the scars to show it,” he said.

Yet Mr. Mearsheimer said Mr. Indyk is “at the core of the lobby,” along with another Clinton administration State Department official, Dennis Ross.

“That is ridiculous,” Mr. Ross said.

He and Mr. Indyk made the point that the American government did not always do what the so-called Israel lobby wanted.

Mr. Indyk, on his way out of the two-hour session, told The New York Sun’s Gary Shapiro that he thought the debate had been “vigorous.” “It exposed a lot of the flaws in Mearsheimer’s paper,” he said.

The start of the event was delayed by more than half an hour as those who had tickets or who were invited guests were scanned by metal detectors.