“The region’s leaders expressed their frustration with the limits and exorbitant costs of current policies and their hunger for a fuller, more creative debate,” said John Walsh, a drug policy analyst at the Washington Office on Latin America, a human rights group.

But the United States has so far rejected legalization as a solution to drug violence.

A State Department spokesman, William Ostick, said the report would be carefully reviewed and discussed with fellow O.A.S. members in Guatemala.

“We look forward to sharing our latest research and experiences on drug prevention and treatment, and to strengthening operational law enforcement cooperation with our partners around the globe in support of our common and shared responsibility for the world drug problem,” he said. “We know other leaders will similarly bring their own data, and anticipate a productive and useful dialogue.”

Kevin Sabet, director of the Drug Policy Institute at the University of Florida, said advocates of drug liberalization were overplaying the significance of the report, which he said contained a lot the Obama administration would agree with.

He said a discussion of legalization was only natural, particularly since two American states, Washington and Colorado, have moved in that direction.

But the report, he said, also suggested that countries in the hemisphere needed to redouble their efforts to fight the impunity of drug gangs, something often overlooked or played down in the debate on the war on drugs. The report notes that drug organizations have atomized into a range of gangs carrying out kidnapping, extortion and other crimes.

“Institutions in the drug-producing nations are going to have to change the way they do business,” Mr. Sabet said. “You cannot only rely on reducing demand and ignore deep-seated institutional problems.”

Mr. Santos, in accepting the report in Bogota, said more study was needed. “Let it be clear that no one here is defending any position, neither legalization, nor regulation, nor war at any cost,” he said. “What we have to do is use serious and well-considered studies like the one the O.A.S. has presented us with today to seek better solutions.”