* Gov't trying to force users off streets into treatment
* Big market for narcotics as Brazil's economy expands
* Action comes ahead of World Cup and Summer Olympics
By Rodrigo Viga Gaier
RIO DE JANEIRO, Jan 10 (Reuters) - A 10-year-old Brazilian boy was hit by a car and killed on Thursday as he fled a drug sweep by police and social workers, reigniting debate over the government's tough response to a surge in crack cocaine use.
The incident occurred around 4 a.m. on one of the main thoroughfares in Rio de Janeiro, Brazil's main tourist destination, the city's social welfare department said in a statement.
The boy, whose name was not released, was part of a large cluster of crack users who scattered as police and social workers approached.
Such clusters are known in Brazil as cracolandias or "cracklands," and dozens have proliferated in big cities such as Rio and Sao Paulo in recent years. Brazil borders the world's top three cocaine-producing countries and has become a huge market for narcotics as its economy expands.
The boy had left home nine days earlier, the welfare department said. His father was dead, and his mother was also a drug user, it said. The boy's 14-year-old brother had found him on Wednesday and failed to convince him to come home.
"Crack is a very violent and cruel drug, and we have to keep working against it," Rodrigo Abel, Rio's undersecretary for social protection, told reporters.
In response to "cracklands" that sometimes see hundreds of people gather to smoke the drug in broad daylight, Rio in 2011 began staging large-scale sweeps to remove addicts from the street.
They are offered drug treatment, although many refuse and quickly go back to using.
Unlike adults, minors are sometimes held for treatment against their will - a practice that has stirred controversy. Rio Mayor Eduardo Paes said last year he would support forced treatment of adults as well.
The sweeps come as Brazil prepares to host the World Cup in 2014 and the Summer Olympics in Rio in 2016.
Twitter and other social media exploded with debate after the boy's death was announced.
"Social cleansing. Police are chasing these crack-using kids as if they were criminals," tweeted Ariel Castro Alves, a Brazilian lawyer specializing in human rights and youth issues.
Emmanuel Fortes, a psychiatrist and vice president of Brazil's Federal Council of Medicine, said the child's death was a tragedy but that the state had little choice but to press ahead given the widespread problem.
"It's a tragedy also to see an entire generation fall victim to this drug epidemic. I understand people are upset by what happened today, but is it correct to leave a 10-year-old on the street to consume drugs?" Fortes told Reuters.
The crisis has led President Dilma Rousseff to massively increase the presence of police and military patrols and even stage drone flights on its borders to halt drug trafficking.
However, Brazil has 10,000 miles (16,000 kilometers) of borders - five times the length of the U.S.-Mexico border - running through Amazon jungle and huge swamps, making it extremely difficult to secure.
Rio's welfare department said it would provide psychological assistance to the boy's family and money for his funeral.