* Extradition of Medellin crime boss sparks turf battles
* City murder rate doubles, violence focused in poor areas
* Faults seen in government's popular security policies
By Hugh Bronstein
MEDELLIN, Colombia, Oct 20 (Reuters) - After a sharp fall in crime that raised hopes of peace in a city once infamous as home to the world's biggest cocaine cartel, the poor neighborhoods of Medellin are once again at war.
The city's murder rate has more than doubled since the 2008 extradition of its main crime boss, known as Don Berna, which left a power vacuum in the local drug and extortion rackets.
"When the boss was here, we had support," a mid-level gangster told Reuters on condition of anonymity. "The difference now is there is no support, so we have to look for it ourselves, and every change (in alliances) causes deaths."
The fight to control the narrow, winding streets of the city's hilltop neighborhoods has descended into a free-for-all involving scores of new gangs run by former right-wing militia members who "demobilized" under a government peace plan.
The violence reveals weaknesses in President Alvaro Uribe's acclaimed security policies as he flirts with running for a third term next year.
Uribe remains popular but the early euphoria over the peace process has not lasted in his home town of Medellin. The local coroner's office has logged more than 1,500 murders so far this year, more than double that in the same period of 2008.
Police dash from one crime scene to another, mostly in poor areas located a safe distance from the affluent neighborhoods that still attract investment and are untouched by the mayhem.
Hundreds of gang members have been arrested, but poverty and the allure of easy money ensures a stream of new recruits.
As international smuggling routes are squeezed by tougher interdiction measures, traffickers are increasingly selling to local users.
"The external market is being closed off to us," the gang boss said. "So, when we have cocaine where are we going to sell it? On the streets. What are we fighting over? Control of those streets."
In the 1980s, Medellin was known as one of the most dangerous places on earth as drug king Pablo Escobar ran an army of enforcers who he paid $2,000 for every police officer they killed.
He was finally gunned down by police on a Medellin rooftop in 1993 and Uribe's security drive brought further improvements in Medellin in recent years, but the new surge in violence shows how tough it is to win the drugs war.
Some crime groups in the city have taken to paying their thugs in cocaine rather than cash, fueling addiction in areas of the city already beset by unemployment.
"This was a calm neighborhood, until now," said the owner of an open air bar where a man was shot dead by two thugs last Friday night in Bello, a Medellin suburb.
An hour later and several blocks away, someone tossed a grenade into a group of gang members sitting by their motorcycles in a park, killing one of them and wounding two.
Uribe, Washington's main ally in left-tilting South America, started negotiating the demobilization of right-wing paramilitaries after his first election in 2002. Thousands of "paras" were seen in televised ceremonies tearfully handing over their guns to government officials.
The process was meant to end violence by paramilitaries who waged an illegal war against Marxist rebels, who still control some rural areas.
But many right-wing militia chiefs, including Medellin's Don Berna, continued managing their crime organizations while negotiating peace. He and others were extradited to the United States on drug charges last year.
"Every major drug trafficking group in Medellin has satellite groups dedicated to murder for hire, extortion of local businesses and the supply of drugs to the local market," said Colombian security analyst Armando Borrero.
"Don Berna was the center of gravity in this solar system," Borrero said. "Without him there to control things, the turf wars have become savage."
Despite the ongoing security challenges, Uribe remains a hero to Colombia's middle class. He says he does not want to cling to power but insists that his policies must stay in place after the end of his current term in August next year.
The Constitutional Court is reviewing a proposal passed by Congress to call a referendum asking voters if they want Uribe to be allowed to run for a third four-year term in May. (Editing by Kieran Murray)