“Cuba, unlike the other countries that are participating, has not yet moved to democracy,” Mr. Obama said. And referring generally to other Latin American countries’ success in overcoming dictatorship and oppression in favor of democracy, Mr. Obama asked “why we would ignore that same principle here.”

Mr. Obama denied acting out of electoral concern over Florida, saying that his position on Cuba had been consistent through his political career. He cited steps that his administration had taken to broaden relations between the American and Cuban people, including allowing Cuban-Americans to send money more freely to relatives in Cuba and to travel there more easily.

The leftist leaders of Ecuador and Nicaragua stayed away from the meeting, at least partly because of the Cuba issue, which also blocked agreement on a consensus statement at the last Summit of the Americas in 2009. Another obstacle this time was Argentina’s unsuccessful demand for language in it that would support its claim of sovereignty over the Falkland Islands, a British dependency in the South Atlantic that Argentina calls the Malvinas. In that dispute, which boiled over into a war between Argentina and Britain in 1982, Mr. Obama said the United States remains neutral.

Before his news conference with Mr. Obama, Mr. Santos told reporters, “The fact there is no declaration is not a failure — just the opposite.” He said that “the fact that these topics were discussed is a success,” and added, “Hopefully within three years we will have Cuba as part of the summit.”

With the backing of several other Latin American leaders, Mr. Santos gave prominence on the summit agenda to a discussion of whether the longtime, United States-led “war on drugs” ought to be replaced with some potentially more effective strategy, perhaps even decriminalization.

The leaders agreed to direct the Organization of American States to name a group of experts to study the issue. President Otto Perez Molina of Guatemala, who favors legalization, said in an e-mail message after the summit that drug use and trafficking was the only topic the leaders discussed at their final closed-door meeting on Sunday. In the discussion, he said, Mr. Obama reiterated his opposition to decriminalization.

“It is a very positive outcome, in the sense that we have to explore what else we can do to find new avenues” to combat the drug trade, Mr. Perez said.