RIO DE JANEIRO, Feb 11 (Reuters) - The war against drugs is failing and the U.S. government should break with "prohibition" policies that have achieved little more than cram its prisons and stoke violence, three former Latin American presidents said on Wednesday.

The respected former presidents urged the United States and Latin American governments to move away from jailing drug users to debate the legalization of marijuana and place more emphasis on the treatment of addicts.

Former Colombian President Cesar Gaviria said there was no meaningful debate over drugs policy in the United States, despite a broad consensus that current policies had failed.

"The problem today in the U.S. is that narco-trafficking is a crime and so any politician is fearful of talking about narco-trafficking or talking about policies because they will be called soft," he said.

Gaviria has joined with former Brazilian President Fernando Henrique Cardoso and former Mexican President Ernesto Zedillo to try to change the debate on drugs in Latin America, where trafficking gangs have killed tens of thousands of people and weakened democracies through corruption.

From Mexico's gang wars to the drug-funded FARC guerrilla group in Colombia and daily shoot-outs between gangs and police in Rio de Janeiro's shantytowns, much of the region is scarred by drug violence and many believe U.S. policies have failed.

A United Nations meeting in Vienna next month will frame international drugs policy for the next 10 years, and the three former presidents, whose group is called the Latin American Commission on Drugs and Democracy, said it is time for change.

They pointed to falling street prices for cocaine and still high levels of consumption in the United States despite decades of policies focused on punishing users and cutting supplies from Latin American countries such as Colombia.

'PREJUDICES, FEARS'

The presidents' commission released a report calling on governments to refocus policies toward treating users, move toward decriminalizing marijuana, and invest more in education campaigns. It said current policies were rooted in "prejudices, fears and ideological visions" that inhibited debate.

Even as the group met in Rio on Wednesday, police arrested 51 people in a major operation in the city and other states against a suspected drug smuggling ring that sent cocaine to Europe and brought back synthetic drugs like Ecstasy.

Organized crime has flourished around drugs and is now threatening the stability of Mexico, where a spiraling war between rival gangs killed more than 5,700 people last year.

Cardoso, one of Latin America's most respected figures, said U.S. leadership was essential to break the cycle of drug-related crime and violence. "It will be almost impossible to solve Mexico's problems and other countries' problems without a more ample, comprehensive set of policies from the U.S. government," he said.

Despite winning power on broad promises of change, drugs policy featured little in U.S. President Barack Obama's election campaign and there are few indications that he will embark on a major overhaul.

Gaviria said Washington appeared increasingly isolated in its repressive approach as Latin America and Europe move toward treating drug abuse as a health problem rather than a crime. (Editing by Raymond Colitt and Kieran Murray)