After he was ousted, Mohammed Mossadegh, head on hands, was found guilty of treason and imprisoned in Iran.

OON after the C.I.A. installed him as president of Guatemala in 1954, Col. Carlos Castillo Armas visited Washington. He was unusually forthright with Vice President Richard M. Nixon. "Tell me what you want me to do," he said, "and I will do it."

What the United States wanted in Guatemala — and in Iran, where the C.I.A. also deposed a government in the early 1950's — was pro-American stability. In the long run, though, neither Colonel Castillo Armas nor his Iranian counterpart, Shah Mohammed Reza Pahlavi, provided it. Instead, both led their countries away from democracy and toward repression and tragedy.

How did this happen? From the perspective of half a century, what is the legacy of these two coups?

Several dozen scholars, including leading experts on Iran and Guatemala, gathered in Chicago this month to consider those questions. Their conclusions were grim. All agreed that both coups — the first that the C.I.A. carried out — had terrible long-term effects.

"It's quite clear that the 1953 coup cut short a move toward democracy in Iran," said Mark J. Gasiorowski, a historian at Louisiana State University who began studying that coup in the 1980's. "The United States bears responsibility for this."

Iranians wrote a constitution and elected a parliament early in the 20th century. Their progress toward democracy stopped after the Pahlavi dynasty took the throne with British help in 1921, but resumed after World War II. By the time of the 1953 coup, Iran was more free than at any time before or since.

The verdict on Guatemala was even harsher. Within a few years after the 1954 coup, Guatemala fell into a maelstrom of guerrilla war and state terror in which hundreds of thousands of people died.

"The C.I.A. intervention began a ghastly cycle of violence, assassination and torture in Guatemala," said Stephen G. Rabe, a historian from the University of Texas at Dallas and author of "Eisenhower and Latin America: The Foreign Policy of Anticommunism."

"The Guatemalan intervention of 1954 is the most important event in the history of U.S. relations with Latin America," Mr. Rabe said. "It really set the precedent for later interventions in Cuba, British Guiana, Brazil and Chile. The tactics were the same, the mindset was the same, and in many cases the people who directed those covert interventions were the same."

President Harry S. Truman authorized creation of the C.I.A. in 1947, and during his administration it carried out covert actions. Truman refused, however, to authorize the overthrow of governments. That changed when Dwight D. Eisenhower became president in 1953.

On Aug. 19, 1953, Prime Minister Mohammad Mossadegh of Iran became the first victim of a C.I.A. coup. Ten months later, on June 27, 1954, President Jacobo Arbenz of Guatemala became the second.

The recent Chicago meeting, at Northeastern Illinois University, was the first time scholars have considered these two coups together. Some of the participants have taken anti-interventionist positions in the past, but all are respected scholars in their fields. Several have devoted years to studying either the Guatemala coup or the one in Iran. Some now see them as constituting a single historical moment, the beginning of an era of C.I.A.-backed coups around the world.

Eisenhower ordered these coups for a combination of economic and political reasons. Elected Iranian and Guatemalan leaders had challenged the power of large Western corporations, Mr. Mossadegh by nationalizing the Anglo-Iranian Oil Company and Mr. Arbenz by forcing the United Fruit Company to sell some of its unused land for distribution to peasants. American officials charged that both were leading their countries toward Communism, but recent research suggests that the likelihood of Communist takeovers in Iran and Guatemala was exaggerated.

Mr. Mossadegh pursued a neutralist foreign policy and cooperated with Communist members of parliament to win approval of social reforms, but was not inclined to socialism. American officials who were assigned to monitor Communist movements in Iran during the 1950's admitted years later that they had routinely overstated the strength of these movements.