By Jeff Franks

HAVANA (Reuters) - Amid hopes tempered by a history of failure, Colombia and the Marxist FARC rebels begin talks in Cuba on Monday in the latest bid to end their bloody, half-century-old conflict.

Tens of thousands of lives have been lost and millions of people displaced in the bitter war the two sides failed to resolve in three past peace attempts, the last ending in 2002.

The negotiations were scheduled to begin on Thursday but were postponed due to "technical" details.

President Juan Manuel Santos, who secretly initiated the peace process almost two years ago, has said there is reason for "moderate optimism" but officials also have warned against unrealistic expectations.

In a recent Gallup poll, 72 percent of Colombians supported the negotiations but only 39 percent thought they would succeed.

The Colombian government and the FARC, or Revolutionary Armed Forces of Colombia, will negotiate five points including rural development, an end to the war, the drug trade, the rebels' future and compensation of victims of the conflict.

Despite past failures, analysts say hopes this time are based on signs of greater flexibility on both sides and a shared need to stop the fighting.

The FARC has been battered by a 10-year-long U.S.-backed military offensive that has halved its ranks to an estimated 8,000 rebels and pushed them deeper into the mountains and jungles that have given refuge since the group formed in 1964.

But it still packs enough punch to continue fighting for years, which threatens the government's plan to open more of the country's remote areas to oil and mining operations that are boosting the economy in the country of 46 million people.

"It's not quite a stalemate, but it feels like it because the likelihood you'd have to keep fighting is high and the cost of that may be greater than the cost of talks," said Adam Isaacson at the Washington Office on Latin America research group.

LAST, BEST CHANCE

He said a weakened FARC may feel this is "their last, best chance to negotiate, that their trajectory is downward."

The last peace talks, held in a tent in the Colombian jungle, turned into a media circus, so both sides have agreed to limit press contacts, a likely reason they are meeting in an undisclosed location in tightly controlled Cuba.

The talks officially began last month in a largely ceremonial meeting in Norway, which has worked behind the scenes with Cuba to set up the negotiations and, along with the Communist island, will serve as a guarantor for the process. Venezuela and Chile will have representatives at the talks.

Santos, who may seek re-election in 2014, wants the process done in nine months but the rebels say peace cannot be hurried.

"These are issues that can't be dealt with in a short time ... above all the social situation in which the people live. There is much poverty in Colombia," FARC lead negotiator Ivan Marquez said in an interview on pro-rebel website www.anncol.eu.

In Norway, he called for ousting foreign companies fueling Colombia's oil and mining boom but his counterpart, Humberto de la Calle, said the talks must stick to the agreed upon topics, the first of which will be rural development.

Numerous potential stumbling blocks await the negotiators, including land reform, decisions on which FARC leaders will be allowed to participate in politics, who must go to jail for the group's crimes and FARC involvement in the drug trade.

In its 48 years of existence, the FARC has transformed from a communist agrarian movement into an organization that deals in cocaine, kidnapping and extortion to sustain itself.

Its leaders deny involvement in the drug trade and declared in February they would no longer kidnap for ransom, but the United States and European Union consider the FARC to be a terrorist organization.

The rebels said they will request a ceasefire at the start of talks, which Santos already has rejected.

(Reporting By David Adams; Editing by Bill Trott)