Ernest Mandel, a Marxist economist at the center of a debate on free speech and academic freedom during the Nixon administration, died on Thursday at his home in Brussels. He was 72.

Dr. Mandel died of a heart attack, said his wife, Anne.

Dr. Mandel won an international reputation in the 1960’s and 70’s for his writings, most notably a 1972 book, “Late Capitalism,” in which he argued that class struggle was affected by long economic waves of 20 to 40 years, rather than by shorter economic cycles.

But he gained a measure of prominence in the United States not so much for his unconventional economic views but because Attorney General John N. Mitchell denied him a visa in 1969, against the advice of Secretary of State William P. Rogers.

The Attorney General acted under a section of the Immigration and Nationality Act of 1952, popularly known as the McCarran Act, that barred visas to those who “advocate the economic, international and governmental doctrines of world Communism” and “who write or publish any written or printed matter advocating or teaching the economic international and governmental doctrines of world Communism.

Dr. Mandel at the time was editor of the weekly leftist journal La Gauche. He had been granted visas in 1962 and 1968, and had violated the conditions of his second visit, apparently unwittingly, by addressing a group that was asked for contributions for the legal defense of French demonstrators.

When Mitchell denied him a visa in 1969, Dr. Mandel was defended by several American scholars, who noted that he had spoken out against the Soviet invasion of Czechoslovakia in 1968, and that he was not a member of the Communist Party.  The visa issue was widely debated in American newspapers, to the apparent surprise of Dr. Mandel.

“It shows that public opinion in the United States is very much alive to the dangers that threaten our basic freedom,” he said.

In March 1971, a Federal Court in New York voted to void Mitchell’s decision, declaring that the United States could not bar a visitor who preached “anarchistic” doctrines.  But on June 29, 1972, the Supreme Court ruled, 6 to 3, that Mitchell had acted within his discretion in denying 
the visa.

Ernest Mandel was born in Frankfurt.  His family moved to Antwerp, Belgium, when he was a child.  During World War II, he was a member of the Belgian Resistance.  He was arrested three times and eventually sent to a work camp.

Since 1940 Dr. Mandel had been a member of the Socialist Fourth International, which was founded by Trotsky in the 1930’s to promote world revolution. After World War II, Dr. Mandel led the Fourth International’s Belgian section.

His revolutionary ideas brought Dr. Mandel into frequent conflict with the authorities, and he was banned at various times from entering France, Germany, Switzerland and Australia.

Dr. Mandel’s last major work, “Power and Money,” was published in 1983.

He is survived by his wife.