* Rebel doubts FARC unity inside Colombia
* Rank-and-file rebels worry about future
* Says commanders mistreat FARC fighters
By Helen Murphy and Luis Jaime Acosta
BOGOTA, Feb 21 (Reuters) - FARC guerrilla fighters hiding out in Colombia's jungles are pessimistic about peace talks in Cuba and increasingly afraid for their future, according to a rebel commander who has just turned himself in.
Alexander Garcia, who deserted the Revolutionary Armed Forces of Colombia this week after 22 years fighting, said military bombardments were demoralizing the rebels even as their negotiators sat down with the Colombian government in Havana.
"There's doubt and uncertainty in the ranks," Garcia told Reuters in the gardens of Colombia's defense ministry days after abandoning the FARC. "What will we do after peace is signed?"
Known by nom de guerre "Caracho," Garcia said he walked for days through thick jungle after leaving 60 of his men in southern Guaviare province as troops closed in, bombing their camp almost daily.
Although a decade of military strikes against the FARC has halved its numbers and put its leadership on the run, defeating the rebels militarily has proved difficult.
Garcia, who had never visited a city before coming to Bogota, said there was little talk in the lower ranks about peace or life outside the FARC, for fear of reprisals from the commanders.
He and his men heard about the negotiations on the radio.
"I doubt anything will come from (the peace talks)," said the unshaven 34-year-old in an interview facilitated by the Colombian government after introducing him to media.
"But if they develop the agenda and there's a happy conclusion, we'll have to see how all the guerrillas are going to be reintegrated."
Garcia joined Latin America's biggest insurgency at the age of 12 in 1991, when the FARC was gaining strength.
Financed in large part by the cocaine trade, the group was able to buy weapons, uniforms and enough food for its growing army of rebel fighters, which by 2000 had reached as many as 17,000.
After the last attempt at peace fell apart in 2002, the government stepped up its offensive, pushing the FARC back into the inhospitable Andean mountains, where it has continued to attack targets such as oil and mining infrastructure that are critical to Colombia's economy.
Garcia commanded two combat units in Guaviare and fought alongside Mono Jojoy, one of the rebels' most feared military leaders until he was killed in a bombing raid in 2010.
"OLD COMMUNIST VALUES GONE"
Military pressure and the death of numerous leaders in the past several years persuaded Garcia to desert, he said.
"The military forces are stronger in everything, in logistics, in training," he said, speaking in a low and cautious tone and declining to elaborate on his rebel activities.
"So many commanders, who were symbols of the guerrillas, have died."
The FARC is now believed to have around 9,000 fighters, its ranks weakened by desertions.
Even if President Juan Manuel Santos' gamble at peace pays off, it will by no means end violence in Colombia as drug trafficking and criminal gangs, many born out of the demobilization of right-wing paramilitary groups, continue to operate across the nation.
Most Colombians believe it will be impossible to absorb fighters like Garcia, many of whom are illiterate, into an already difficult job market. Preventing the rebels from joining crime gangs could be the toughest challenge of peace.
Once Colombia's military intelligence officers decide that Garcia has told them everything useful he knows, and media interest in his case dies down, he may struggle to find a place outside the FARC, which is known for strict discipline and intolerance for insubordination.
Surrounded by troops, who often parade senior deserters in public, and looking uncomfortable with being questioned, Garcia said he doubted the unity of the FARC commanders, even as negotiators in Havana defend the tight leadership.
It was unclear if Garcia felt obliged to make some comments that he thought might please Colombian authorities.
He said poor treatment by mid-level rebel commanders, as well as a ban on family visits and poor health in the lower ranks, had "created a very different concept of what it is to be part of the guerrillas."
"There's a loss of ideology in the guerrilla movement; there's a leadership problem because some commanders treat the troops very badly," said Garcia, wearing a San Antonio Spurs cap. "The old communist values no longer exist."
Garcia's description of an unhappy life in the FARC contrasts with the official line from its leadership, who insist the rank-and-file remain enthused and ready to fight on for years to achieve social justice should the peace talks fail. (Editing by Daniel Wallis, Andrew Cawthorne and Doina Chiacu)