By Tim JohnsonMEXICO CITY -- Voters in Colorado and Washington state who approved the recreational use of marijuana Tuesday sent a salvo from the ballot box that will ricochet around Latin America, a region that's faced decades of bloodshed from the U.S.-led war on drugs.Experts said the moves were likely to give momentum to countries such as Uruguay that are marching toward legalization, to undercut Mexican criminal gangs and to embolden those who demand greater debate about how to combat illegal substances."The trend is toward legalization," said Jorge G. Castaneda, a former Mexican foreign minister who's an advocate for decriminalization.The decision by voters in Colorado and Washington to legalize marijuana for recreational use puts those states -- the first to approve outright legalization -- at loggerheads not only with the federal government but also with global treaties that label marijuana a controlled substance.Taking a lesser step, Massachusetts voters approved a measure that allows the medical use of marijuana, joining 17 other states and the District of Columbia in permitting such limited usage.U.S. diplomats in Latin America said Wednesday that President Barack Obama would hold firm against efforts to soften drug laws."The government of my president is totally against any initiative that weakens rules or laws on the sale or offering of illegal drugs," P. Michael McKinley, the U.S. ambassador to Colombia, told Caracol Radio there.But contradictory policies at the state and federal levels in the United States may throw the door open to more intense debate about U.S.-led pressure to respect international narcotics treaties."Politically and symbolically, this is really powerful. My guess is that this will accelerate some countries' efforts to have a legal marijuana regime," said Alejandro Hope, a former ranking official in Mexico's civilian intelligence service who studies the economic impact of marijuana smuggling in Mexico.Uruguay, a small South American nation led by a former leftist guerrilla, has moved ahead since August on a proposal to legalize marijuana under a government monopoly."Chile also has a bill before its Congress. I'm guessing that Argentina may also follow suit. This will go from south to north," Hope said.He added, however, that change would come over years, not months."We need to tamp down some of the expectations. None of this will happen quickly," he said.Castaneda concurred, saying marijuana legalization remains "a radioactive issue" and the contours of the debate will change only with time.Experts said nations -- or states within nations -- couldn't easily buck global treaties that included marijuana as a criminal substance."It's a direct breach of the 1961 U.N. convention on narcotic drugs," said Martin Jelsma, a Dutch scholar on drug control laws at the Transnational Institute, a center in the Netherlands that advocates for less punitive global drug policies.Jelsma said nations and states "will have to find a way to reconcile" their laws with the global treaty, which has some 190 signatories. Some may choose to follow the path of Bolivia, which said in the middle of last year that it would withdraw from the convention to protest the U.N. classification of coca leaf as an illegal substance. Many indigenous people in the Andes chew coca leaf as a medicinal and social practice.Others who push for global decriminalization of marijuana laws also said that U.S. efforts to pressure foreign nations over marijuana would weaken."It really is a game changer. It places the U.S. in a very different place," said Kasia Malinowska-Sempruch, the director of the global drug-policy program of the Open Society Foundation, a New York-based group funded by liberal financier George Soros. "This clearly says the paradigm is shifting."Jelsma said that if U.S. states such as Colorado and Washington could impose a regime of control on marijuana that didn't cause usage to soar, "it could mark a snowball effect on Latin America."Among those unhappy with moves to legalize marijuana are likely to be Mexican organized-crime groups, which earn billions of dollars a year smuggling pot to the United States. A study published last month by the Mexican Institute for Competitiveness, a nonpartisan research center that examines the effects of globalization, said that as much as a third of crime groups' revenue came from smuggling pot.Hope, a co-author of the study, said crime groups, particularly the powerful Sinaloa Cartel, could "lose 24 percent of their gross export revenues" as U.S. states softened laws on marijuana."This would reshape the Mexican criminal underworld in interesting ways," he said, including slashing the number of jobs involved in smuggling an estimated 2,000 tons of marijuana northward each year.Hope said, however, that the impact would be biggest in the political sphere."This will embolden some voices in the Americas calling for a change in policies," he said.Several former Latin presidents have signed statements criticizing U.S. counter-drug policy, including former President Fernando Henrique Cardoso of Brazil, former Colombian leader Cesar Gaviria and former Mexican President Ernesto Zedillo, all of whom have called for legalizing marijuana.Castaneda, who also has signed the statements, said U.S. pressure on Latin nations to deploy soldiers to fight drugs would look inconsistent as some states allowed residents to use marijuana legally."It will look more and more contradictory, and even aberrant, that on one hand Mexico racks up 60,000 dead under [President Felipe] Calderon while on the other side Americans are going for legalization of, at least, marijuana," he said.