* Latin America consensus shifting toward more lax laws
* 60,000 Mexicans killed in drug violence since 2006
By Brian Winter
UNITED NATIONS, Sept 26 (Reuters) - The presidents of Mexico, Colombia and Guatemala all called for a vigorous global debate of anti-narcotics laws at the United Nations on Wednesday, raising new questions about the wisdom of the four-decade-old, U.S.-led "war on drugs."
Although none of the leaders explicitly called for narcotics to be legalized, they suggested at the U.N. General Assembly that they would welcome wholesale changes to policies that have shown scant evidence of limiting drug flows while contributing to massive violence throughout Latin America.
"It is our duty to determine - on an objective scientific basis - if we are doing the best we can or if there are better options to combat this scourge," Colombian President Juan Manuel Santos said.
Mexican President Felipe Calderon, who leaves office on Dec. 1 after spending much of his presidency locked in a bloody battle with drug-smuggling gangs, called on the United Nations to lead a global debate over a less "prohibitionist" approach to drugs.
Guatemala's President Otto Perez Molina echoed Calderon's call and went even further, saying that "the basic premise of our war against drugs has proved to have serious shortcomings."
The speeches, which were a few hours apart, constituted some of the most public challenges to date of anti-drug policies that have been mostly unchanged since the 1970s.
Mexico and Colombia are two of Washington's firmest allies in Latin America and both work closely with U.S. anti-drug efforts. While the subject of legalization was discussed at an Americas-wide summit in Colombia attended by U.S. President Barack Obama earlier this year, raising the once-taboo subject at the 193-nation meeting in New York amounts to an escalation of the debate.
Obama has ruled out any major changes to drug laws, but some U.S. diplomats privately concede that the consensus around Latin America is clearly swinging against the status quo, and that some degree of change is imminent.
All three leaders were careful to say they were not proposing giving in to smuggling gangs that have made Latin America one of the world's most violent regions. Mexico has been particularly hard hit in recent years, with an estimated 60,000 people killed in drug-related violence during Calderon's six-year term as he attempted to crack down on cartels.
"We won't cede an inch" to the gangs, Calderon said.
Calderon and Santos have suggested on other occasions that they might be open to legalization of narcotics if that helped reduce violence.
Colombia remains one of the world's biggest producers of cocaine despite a decade of U.S.-sponsored eradication efforts, while Mexico has seen unprecedented violence as a transit point for drugs into the United States, the world's biggest consumer of narcotics.
An influential group of former Latin American leaders including Brazilian ex-President Fernando Henrique Cardoso has openly advocated decriminalization of some drugs as a way to reduce violence.
The small, relatively prosperous South American nation of Uruguay has gone the furthest, sending a bill to Congress last month that would allow the state to grow and sell marijuana.
In his comments on Wednesday, Santos described the debate over drug policy as "a discussion that the world has avoided for many years, and one we hope will produce concrete results."
"The debate on drugs must be frank, and without a doubt, global," Santos said.
Calderon repeated his calls for Washington to tighten gun controls to stop weapons flowing from the United States into the hands of Mexican drug cartels. He has also urged Washington to revive a ban on assault weapons in the United States that expired in 2004.