CARTAGENA, Colombia— President Barack Obama arrived Friday for a hemispheric summit hoping to talk up U.S. exports to the region, but he is being greeted by a subtle revolt against American antidrug policy and a host of complaints the White House would just as soon avoid.

The uprising on drug policy is led by some of Washington’s closest and best-funded allies in Latin America, including Colombia, who are openly advocating for a discussion of legalization or decriminalization of the illegal drugs that have ravaged the region.

The matter will be on the agenda for this weekend’s Summit of the Americas, a weekend gathering of 32 heads of state.

Drugs won’t be the only uncomfortable issue for Mr. Obama, who remains popular throughout Latin America but must face leaders increasingly willing to challenge the U.S. He also will confront opposition to U.S. policy toward Cuba, frustration with U.S. failure to overhaul its immigration laws and a general sense in Latin America that the U.S. has grown disengaged from its own neighborhood.

Ahead of the meeting, U.S. officials played down the thorny issues, instead portraying the summit as an opportunity to promote trade, a politically useful approach given election-year concerns about the pace of economic recovery.

Mr. Obama made that point Friday, stopping en route to Colombia to tout the benefits of trade outside a major port in Tampa, Fla., the largest swing state up for grabs in November. Mr. Obama linked economic growth in Latin American countries to increased U.S. trade in the region, tying both back to American jobs, a chief re-election issue. “We want them spending money on American-made goods so that American businesses can put more people back to work,” he said. “So while I’m in Colombia talking with other leaders, I’m going to be thinking about you.”

After years of delay, the U.S. last year ratified free-trade agreements with Colombia and Panama. Mr. Obama said those agreements helped set the U.S. on track to meet his goal of doubling exports by the end of 2014, and announced a new Small Business Network of the Americas to promote trade for small and medium-size businesses throughout the region.

Even so, some business leaders and experts say the U.S. has little in the way of a comprehensive trade agenda for the region, particularly with the largest economy, Brazil.

When Mr. Obama attended the Americas summit three years ago, the newly inaugurated American president was greeted warmly. He responded that the U.S. had at times been disengaged and promised a relationship based on equal partnership.

Since then, Latin American leaders have felt neglected, particularly as Mr. Obama’s launched a drive last year to intensify his focus on Asia. “In the region there’s pretty broad disappointment with the lack of attention,” said Cynthia Arnson, director of the Latin America Program at the Washington-based Wilson Center think tank.

Regional leaders for the first time are openly questioning drug policies molded by Washington. Colombian President Juan Manuel Santos, whose country remains the world’s top cocaine producer despite a large-scale effort to destroy coca crops, put the question of legalization onto the summit’s agenda, and has called for a closer examination of the costs and benefits of the decriminalization of personal consumption.

Mexican President Felipe Calderón, who declared war against Mexico’s drug cartels in 2006, regularly blames his country’s brutal narcotics-related violence on drug consumption in the U.S., and has suggested that Washington needs to retool its antidrug policy. And Guatemalan President Otto Pérez Molina, a retired general who has seen his country become easy prey for drug cartels fleeing Mexico, has called for a wide push to decriminalize drug use.

“More than 40 years after the world began this war against drugs, I think we need to analyze whether what we are doing is correct,” Mr. Santos told Colombia’s leading daily, El Tiempo.

The shift was led by a blue-ribbon panel of former Latin American statesmen who called Washington’s antidrug efforts a failure and advocated the decriminalization of marijuana.

“It is no longer radioactive for leaders in Latin America to say that prohibition is not the only answer,” said Moises Naim, a fellow at the Carnegie Endowment for International Peace. “I think 2012 will go down in history as the year when the pillars of Washington’s drug policy began to erode.”

Ahead of the summit, the Obama administration made it clear that it isn’t interested in a policy change. “It’s worth discussing,” Vice President Joe Biden said last month in Mexico. “But there is no possibility the Obama-Biden administration will change its policy.”

But White House officials say the conversation about legalization could be useful in explaining how many problems an approach like this would generate. “It helps demystify this as an option,” said Dan Restrepo, senior director for the Western hemisphere.

While a change in U.S. drug policy isn’t likely, the summit could trigger subtle changes in the region. Colombian Foreign Minister Maria Angela Holguin, for example, said a joint-task group to examine the region’s drug policies and propose some changes could emerge from the weekend meeting.

—Carol E. Lee
and José de Córdoba contributed to this article.