For the first time since the United States launched its “war on drugs” four decades ago, there are signs that the forces supporting legalization or de-criminalization of illegal drugs are gaining momentum across the hemisphere.

Granted, this is a debate that is just starting at government levels, and that will take years to produce concrete results.

But there are several new factors, including a reduction of U.S. anti-narcotic aid to Latin America proposed by the Obama administration in its 2013 budget announced last week, that are beginning to pose an increasingly serious challenge to the traditional interdiction-based U.S. anti-drug strategies.

Consider:

l First, for the first time, Latin American presidents currently in office are openly calling for government-to-government talks to discuss legalization or decriminalization of illicit drugs.

Last week, Guatemalan President Otto Perez Molina said he will propose to his Central American counterparts to legalize drugs in the region and to decriminalize the transportation of drugs through the area.

“I want to bring this discussion to the table,” Perez Molina was quoted as saying by the Associated Press. “It wouldn’t be a crime to transport, to move drugs. It would all have to be regulated.”

Aides to Perez Molina tell me that he will bring it up at a pre-scheduled meeting of Central American countries next month.

Until now, several former presidents — Vicente Fox and Ernesto Zedillo of Mexico, Fernando Henrique Cardoso of Brazil and Cesar Gaviria of Colombia, among them — have signed statements calling for the legalization or decriminalization of drugs, but they only did it once they had left office. The current presidents of Mexico and Colombia say they are open to discuss the issue, but that they will not lead the pack.

l Second, simultaneously, the United States plans to reduce its anti-drug aid to Latin America by 16 percent next year, according to the 2013 budget the Obama administration sent to Congress last week.

According to the budget proposal, U.S. narcotics control and law enforcement funds to Mexico would be cut by nearly $50 million, or 20 percent from last year’s levels, while anti-drug funds to Colombia would drop by 11 percent, and to Guatemala by 60 percent.

Supporters of the U.S. aid cuts say the decline reflects in part Latin American countries’ growing capabilities to fight the drug cartels by themselves. Critics dispute that, saying that it’s hard to argue that Mexico and Guatemala, among others, need less foreign anti-drug aid.

l Third, while there is no movement on this issue in the U.S. Congress, pro-decriminalization forces in the United States are making significant progress at the state level.

There are already 13 states that have approved use of marijuana for medical purposes, and three others will propose it in state ballots in the November election.

In addition, some experts predict that California’s Proposition 19 marijuana legalization initiative, which lost by 8 percent of the vote in 2010, is likely to pass in November. Their reasoning: more young people — who tend to support legalization — will vote in this year’s general election in California than they did in the 2010 mid-term election.

Before concluding this column, I asked University of Miami professor Bruce Bagley, an expert on U.S. drug-policies in Latin America, how he sees the various challenges against the traditional interdiction and prohibition-based U.S. drug policies.

“This is becoming a kind of avalanche,” said Bagley, who supports decriminalization of marijuana. “There is a growing questioning of the hard-line drug policies both in Latin America and here in the United States.”

Bagley added, “Prevention, education, treatment and rehabilitation programs are more effective than drug-supply repression.”

My opinion: I agree. Granted, decriminalization of marijuana would bring about an increase of consumption at the beginning. Most studies show that when the United States lifted the prohibition against alcohol, the price of alcohol went down, and consumption went up. The same may happen with drugs.

But most studies also show that — much like happened with cigarette smoking — effective campaigns can dramatically reduce drug consumption, without the sequel of domestic crime epidemics and “wars,” such as the ones that are leaving tens of thousands of deaths a year in Mexico and Central America’s drug-related violence.

Until now, this was a debate that was limited to former presidents, academics and journalists. Now, it’s beginning to make its way into government houses.