By MARTHA MENDOZA

Vice President Joe Biden heads to Latin America Sunday amid unprecedented pressure from political and business leaders to talk about something U.S. officials have no interest in debating: decriminalizing drugs.

Presidents of Costa Rica, Guatemala, El Salvador, Colombia and Mexico, all grappling with the extremely violent fallout of a failing drug war, have said in recent weeks they'd like to open up the discussion of legalizing drugs. Argentina, Uruguay, Peru and Mexico already allow the use of small amounts of marijuana for personal consumption, while political leaders from Brazil and Colombia are discussing alternatives to locking up drug users.

Business leaders are weighing in as well: in February, a group of banking, medical and legal experts sponsored a drug policy conference in Mexico City which concluded that current drug control policies aren't working and need reform.

"It's a different moment when you have actual heads of state talking about the need for a thorough debate on this," said John Walsh, a drug policy expert at the Washington Office on Latin America, an independent think tank. "It's certainly different for sitting presidents to be uttering those words. You wouldn't have thought it possible just a few years ago."

Dan Restrepo, the top Latin America official in the White House, briefing reporters about Biden's upcoming trip, said the vice president does expect a "robust conversation" about the security problems Latin American countries face as drug traffickers battle to control the lucrative U.S. sales. But he said Latin American leaders shouldn't expect a shift in policy.

"The Obama administration has been quite clear in our opposition to decriminalization or legalization of illicit drugs," said Restrepo.

Biden is scheduled to arrive in Mexico City on Sunday to discuss economic and security issues with Mexican President Felipe Calderon. He also plans to meet Monday with the three top Mexican presidential candidates running for a six-year term to replace Calderon this year.

On Tuesday Biden is slated to travel to Honduras to meet President Porfirio Lobo, along with the presidents of El Salvador, Panama, Costa Rica and Guatemala, all countries struggling with the sweeping consequences of expanding drug cartels. Drug gangs have killed tens of thousands, overcrowded prisons are overflowing with accused drug users while powerful cartels fuel corruption — influencing elections, weakening democracies and threatening fragile economies.

"I do think that the issue of legalization will be raised by the leaders to Biden, but in private," said Walter McKay, a policing expert on security issues in Mexico, where more than 47,500 people have been killed in drug gang violence since 2006.

Two weeks ago, Guatemala's president Otto Perez Molina, a right wing conservative and former army general, stunned observers when he declared the U.S. inability to cut illegal drug consumption leaves his country with no option but to consider legalizing the use and transport of drugs. He vowed to galvanize regional support.

Since then, Costa Rican President Laura Chinchilla and El Salvador's President Mauricio Funes have said they're open to the discussion, while Panama's leaders say they do not agree with decriminalizing drugs.

For decades Latin Americans leaders and the U.S. have cooperated on a war on drugs, with more than a trillion dollars spent by the U.S. to support enforcement and eradication in Latin America, as well as promises to reduce cocaine, marijuana and methamphetamine use in the U.S. that generates an estimated $25 billion in profits each year.

But during that time, demand for drugs has increased, fueling violent competition between dealers.

In 2009, former presidents of Mexico, Brazil and Colombia blasted the war on drugs and said it was time to consider the decriminalization of marijuana. Last summer they were joined by more than a dozen high level international leaders including former U.N. Secretary-General Kofi Annan and former U.S. officials George P. Shultz and Paul Volcker, again slamming the war on drugs as a failure and calling on governments to undertake experiments to decriminalize the use of drugs, especially marijuana, to undermine the power of organized crime.

But while it's one thing for former presidents to suggest decriminalizing drugs, it is another thing entirely when sitting presidents do so, said retired Brazilian judge Maria Lucia Karam in an email to The Associated Press.

Karam said that while Latin American leaders at first may have been willing to give the "get tough" strategy time to work, they've been worn down by the drug war's relentless toll.

"The public comments we are seeing are a sign of deep frustration and anger that is now prevalent in Latin America due to the U.S. and U.N.'s seeming unwillingness to engage in a serious debate about implementing effective drug policies that respect human rights and truly protect health," she said.

Danny Kushlick, who heads the London-based Transform Drug Policy Foundation, said the region is "on the verge of a tipping point that will begin when the Latin Americans raise the issue within earshot and in full view of the Americans. Ultimately this is about allowing democratic conversations to take place without being leaned upon by the U.S."

But former U.S. drug czar John Walters said those who are calling for a debate on legalization are taking a dangerous and misguided step.

"I would note to them that the kind of dangerous people they face would welcome that change, to become more powerful," he said. "Legalizing is not a solution, it's an excuse."

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Associated Press writers Marcos Aleman in El Salvador, Romina Ruiz in Guatemala and Freddy Cuevas in Honduras contributed to this report