Ernesto F. Betancourt, 83, a Cuban-born former ally of Fidel Castro who quickly became disenchanted with the autocratic leader and led a decades-long publicity campaign against him, died June 20 at his home in Bethesda after a heart attack.

As a Castro opponent, Mr. Betancourt found his greatest platform as director of Radio Marti, a federal government station that broadcasts to Cuba and is named for Cuban independence seeker Jose Marti.

Mr. Betancourt joined the radio station in 1985, shortly after its inception, and served as its director until 1990. Later, he co-hosted a biweekly program on Radio Marti and wrote scores of newspaper opinion essays assailing Castro’s leadership.

From 1960 to 1975, Mr. Betancourt worked at the Organization of American States, a social and economic development grouping made up predominantly of Latin American countries, as director of budget and finance and director of organizational development.

For many years afterward, he was an independent public administration consultant who worked on projects with the World Bank, International Monetary Fund and the Inter-American Development Bank. He retired in 2006.

Ernesto Francisco Betancourt was born in Havana on Nov. 7, 1927. His father was an American citizen, and the younger Betancourt came to the Washington area in the late 1940s to attend American University. He received a master’s degree in public and international affairs from the University of Pittsburgh in 1973.

In Washington, he joined Castro’s revolutionary group, the 26th of July Movement. He registered as a foreign agent with the Justice Department in 1957 and, for the next two years, issued statements on behalf of Castro in the United States.

When Cuban dictator Fulgencio Batista fled the country, Mr. Betancourt and other rebels with allegiances to Castro took over the Cuban Embassy in Washington on Jan. 1, 1959.

He accepted a position in Castro’s new government in Havana as managing director of the Cuban Bank of Free Trade. In April 1959, Mr. Betancourt escorted Castro on an official trip to Washington, serving as the leader’s personal adviser.

Mr. Betancourt said he broke with the Castro regime the following July. During a meeting with banking leaders, Castro said he was going to depose of Manuel Urrutia, the first president of post-revolutionary Cuba, even if such a move provoked American intervention.

“Well, if they send the Marines, I don’t care,” Mr. Betancourt recalled Castro saying. “They will have to kill between 300,000 and 400,000 Cubans, and I will get a bigger monument than Jose Marti.”

Mr. Betancourt said that after he went home that night, he told his wife, “I had not joined the revolution to be a grain of sand in anybody’s monument.”

Mr. Betancourt resigned from the government a few months later, and he and his family went into self-imposed exile in the United States.

He wrote “Revolutionary Strategy: A Handbook for Practitioners” (1991) and several books about Cuba.

Survivors include his wife of 62 years, Raquel Prieto Betancourt of Bethesda; four children, Adela Jabine of Silver Spring, Ernest Betancourt of Bethesda, Luis Betancourt of Harrisonburg, Va., and Beatriz Hardy of Williamsburg, Va.; a brother, Roger Betancourt of Kensington; and a granddaughter.