* Peace talks with rebels to begin in Norway this week
* Every past negotiation has ended in failure
* FARC guerrillas at weakest point in decades
By Jack Kimball
BOGOTA, Oct 14 (Reuters) - Colombia's government and Marxist rebels will sit down this week to start peace talks aimed at ending nearly half a century of conflict after a 10-year military offensive against the guerrillas failed to deliver a coup de grace.
President Juan Manuel Santos is attempting what many other leaders have tried but failed to do in the past - reach a negotiated deal with the Revolutionary Armed Forces of Colombia (FARC) and bring peace to Latin America's No. 4 economy.
The former defense minister has seen his popularity slide over the last year with former President Alvaro Uribe, for long a close ally, leading criticism that Santos has been too soft on the FARC. But a peace agreement before the next election in 2014 would all but guarantee Santos a second term.
While security has improved by leaps and bounds since a U.S.-backed offensive against FARC rebels and drug barons began a decade ago, the security forces have been unable to land a decisive blow. The FARC is still a threat and, although weakened, it has stepped up its attacks in the last few years.
Analysts say it is clear the conflict cannot be won by military means alone and the government has a greater chance of negotiating an end to the war from a position of strength than of completely wiping out the rebels.
"We take on these talks with moderate optimism but with the absolute conviction that it is an opportunity that we cannot waste," Santos told the U.N. General Assembly late last month.
Nearly two years of secret talks in Cuba led to the formal discussions, which start in Norway this week and then move to Havana. Santos hopes the peace process can be successful within months.
For many in rural Colombia, the stakes could not be higher.
"We're the ones who suffer, our families, our parents," said
Sara Munoz, a 39-year-old mother of two children who is selling her house to get away from the violence in the province of Cauca. "We have to leave our houses, leaving our homes abandoned to flee to another part because we have children."
At primary schools in Cauca, school children have regular safety drills, falling to the ground and huddling together as teachers mimic the sound of gunfire outside.
There is still frequent fighting in the province and Colombian troops that patrol its unpaved roads in armored vehicles nickname it "Cauca-kistan," comparing the fighting there with the war in Afghanistan.
Rumors of talks with the FARC - Colombia's largest insurgent group - have swirled since Santos took office in 2010 and he made early steps to kick-start a peace process with reforms giving land back to peasants displaced by the conflict and paying reparations to its victims.
The failure of the last round of talks a decade ago, when the government ceded territory the size of Switzerland to the FARC and still couldn't reach a deal, hangs over Santos' head, but he insists he won't repeat past mistakes.
Aware he cannot afford to be seen as soft, Santos has refused the FARC's call for a ceasefire once the peace talks start and instead vowed to step up military operations.
The talks will focus mainly on land reform, drug trafficking and political participation.
Possible sticking points include deciding which FARC leaders will be allowed to participate in politics, who will or will not go to jail for war crimes, and what can be done on land reform since every attempt since the 1960s has failed.
Security guarantees will also be crucial as the rebels remember the mass murder of members of the Union Patriotica - a political party accused of links to the FARC - in the 1980s by right-wing death squads.
Right-wing paramilitary groups formed in the 1980s to protect wealthy landowners and drug traffickers from rebels complicated previous efforts to negotiate peace but they have demobilized in the last few years.
Some mid-level former commanders have morphed the old structures into new drug gangs with links to their former enemies, the FARC. They are more concerned with business now than ideology, but could still cause problems as the government tries to pacify the country.
There are also worries about divisions within the FARC and a possible fragmentation if the peace talks advance, e specially in the guerrilla army's powerful southern front, which is heavily involved in the drug trade.
The ultra-right and ultra-left "are hard obstacles because here there is not only debate but shooting," said Leon Valencia, a former member of a small rebel group who now heads the Nuevo Arco Iris think-tank.