Biden, on a two-day swing to Mexico and Central America, said a sour mood over violence from powerful narcotics mafias has led to a desire in some corners of Latin America to debate legalization.

"It warrants a discussion. It's totally legitimate for this to be raised," Biden said, adding that he'd spent "thousands of hours" at Senate hearings over the issue.

But Biden said that even if drug legalization might have benefits like reducing prison populations, it also would engender health problems, expand drug usage and even create bureaucracies for drug distribution.

"It impacts on a country's productivity. It impacts on the health costs of that country. It impacts on mortality rates. It's worth discussing," Biden told a group of journalists. "But there is no possibility that the Obama-Biden administration will change its policy on legalization."

On Tuesday, Biden travels to Honduras, where his aides promise a "robust" working lunch discussion with Central American presidents - several of whom support alternative policies, including drug legalization, to deflate powerful drug gangs that have turned the isthmus into the most murderous region on the planet.

The calls for debate on legalization amount to a cry for help from countries battling the menace of Mexican and Colombian drug gangs moving into Central America.

Leading the charge is a surprising paladin: right-wing Guatemalan President Otto Perez Molina, who surprised Washington after his inauguration two months ago with diplomatic efforts to rally support for a legalization debate.

His posture has garnered support, including from Costa Rican President Laura Chinchilla, who said the issue should no longer be taboo.

"Central America has the right to debate and the right to discuss this as long as it is done with rigor and seriousness, and that is the intention," Chinchilla said last Wednesday after meeting with Perez Molina's envoy, Vice President Roxana Baldetti.

Perez Molina and Chinchilla will be at Tuesday's lunch with Biden, along with presidents of El Salvador, Honduras, Nicaragua and Panama.

Some political analysts suspect that Perez Molina, a former military intelligence chief, pushes an issue that remains largely anathema in U.S. politics to capture Washington's attention, ignoring the practical implications of such a policy swing at home.

"Can you imagine? Eighty percent of Guatemalans are not in favor of decriminalizing drugs. How would a government push such an unpopular measure?" asked Raquel Zelaya, an economist at the Asies think tank in Guatemala City.

Yet some regional leaders - Mexican President Felipe Calderon prominent among them - voice deepening frustration at high U.S. drug demand, flows of drug profits and weapons southward, and the seeming contradiction between American pressure for harsh suppression measures in Latin America while, in the United States, a growing number of states permit medical marijuana.

On Monday, Biden met Calderon for two hours and later interviewed the three leading candidates vying to replace him in elections scheduled for July 1.

Last week, speaking to attorneys general and defense ministers from around the hemisphere, Calderon said that Mexico has captured 22 of its 37 most-wanted criminals, seized 562 aircraft, and done its share in battling drug cartels.

But unless the United States urgently slashes the flow of profits for drug gangs, or cuts back on domestic drug use, it should implement "alternative public policies" on narcotics, Calderon said. The reference to legalization was oblique, as Calderon is wary of endangering U.S. counter-drug support under Plan Merida, an umbrella aid plan for $1.6 billion.

Despite Biden's emphatic rejection of moves toward legalization, analysts of counter-drug policy say policymakers in Washington may no longer be able to halt demand for broader discussions.

"What's clear is that for the U.S. to continue to say, 'There is no debate and discussion to be had. It's a settled matter' - that won't fly anymore," said John Walsh, drug policy program coordinator at the Washington Office on Latin America, a social justice and human rights advocacy group.

Demands to address failures in U.S.-designed counter-drug policies have been stimulated, ironically, by the posture of Washington's closest ally in the region - President Juan Manuel Santos of Colombia, who said last fall that he would welcome discussion about legalization but would be "crucified" if he led the charge.

Santos, head of a South American coca-growing country that has paid a heavy toll for battling drug cartels over three decades, will host the April 14-15 Summit of the Americas in Cartagena, Colombia, and has indicated counter-drug strategies should be debated then.

President Barack Obama is expected to attend the summit.

In Mexico and throughout Central America, people are growing weary of the death tolls from organized crime.

Mexico has tallied more than 50,000 murders since late 2006, and the United Nations Office on Drugs and Crime said in October that murder rates in Honduras and El Salvador are the highest in the world, putting Central America at "a crisis point."