CARTAGENA, Colombia — President Obama will highlight trade and business opportunities in Latin America at a regional summit in Colombia this weekend, but other leaders may upstage him by pushing to legalize marijuana and other illicit drugs in a bid to stem rampant trafficking.

Obama, who opposes decriminalization, is expected to face a rocky reception in this Caribbean resort city, which otherwise forms a friendly backdrop for a U.S. president courting Latino voters in an election year. But the American demand for illegal drugs has caused fierce bloodshed, plus political and economic turmoil, across much of the region.

Colombia’s president, Juan Manuel Santos, wants the 33 leaders at the Summit of the Americas to consider whether the solution should include regulating marijuana, and perhaps cocaine, the way alcohol and tobacco are. Other member states also are calling for that dialogue despite the political discomfort it may cause Obama back home.

“You haven’t had this pressure from the region before,” said Michael Shifter, president of the Inter-American Dialogue, a think tank in Washington. “I think the [Obama] administration is willing to entertain the discussion, but hoping it doesn’t turn into a critique of the U.S. and put the U.S. on the defensive.”

Obama also is expected to take flak from leaders frustrated by the lack of U.S. movement on two other troublesome issues, immigration reform and the long-standing embargo of Cuba. Cuban leaders are not participating in the summit, but many regional governments oppose the U.S. policy of embargo.

In internal debates, White House officials have weighed the risk of talking about decriminalization, which is still taboo for many U.S. voters, against concern about alienating leaders who bear the brunt of the battle against the heavily armed cartels that supply most marijuana, cocaine and methamphetamines to U.S. markets.

White House officials say Obama will not change his drug policy. They hope to keep talk of legalization behind closed doors while he focuses publicly on other tactics, including improving security forces, reforming governance and enhancing economic opportunities.

The call for change comes from front-line veterans of the drug wars, including Colombia. Santos says he has the moral authority to seek new solutions because his country’s citizens and security forces have spilled so much blood fighting drug traffickers.

Also leading the charge isGuatemala’spresident, Otto Perez Molina. After a pre-summit meeting with leaders of Costa Rica and Panama, he called for a “realistic and responsible” discussion of decriminalization in Cartagena.

“We cannot eradicate global drug markets, but we can certainly regulate them as we have done with alcohol and tobacco markets,” he wrote in the British newspaper the Observer on April 7.

White House officials plan to argue that no evidence indicates legalization would slow the flow of narcotics or reduce drug-related killings. Vice President Joe Biden offered a preview in Miami Beach last month.

“We should have this debate, and the reason is to dispel some of the myths that exist about legalization,” Biden told reporters. “There are those people who say, ‘If you legalize, you are not going to expand the number of consumers significantly.’ Not true.”

U.S. officials also will emphasize administration efforts to reduce illicit drug use in the United States, the world’s largest consumer of cocaine and other illegal drugs.

The Justice Department, for example, has added special courts that can sentence drug abusers to treatment programs instead of prison. And the Patient Protection and Affordable Care Act, assuming it survives Supreme Court review, requires the medical industry to treat substance abuse as a chronic disease.

Marijuana use in America has increased by 15% since 2006, but cocaine use has dropped by 40% in that time, according to theU.S. Department of Health and Human Services. Experts say the global market for cocaine is unchanged because use in Europe more than doubled in the last decade.

The idea of regulating and taxing the production and sale of illegal drugs isn’t new. A panel led by former United Nations Secretary-General Kofi Annan and past presidents of Mexico, Brazil and Colombia concluded in a report in June that the drug war had “failed” and recommended easing penalties for farmers and low-level drug users.

That doesn’t make the issue any easier for Obama.

“I don’t think anybody thinks the current policy works right now, but public opinion hasn’t gotten to the point of accepting the idea of legalization,” said David Damore, a political scientist at the University of Nevada-Las Vegas who writes about U.S. and Latino politics. “There’s nothing to be gained from it politically, and it opens you up to an attack.”

cparsons@latimes.com

brian.bennett@latimes.com

Parsons reported from Cartagena and Bennett from Washington.