* Santos says runoff a vote a choice between fear, hope
* Zuluaga says Santos has pandered to the FARC
* Zuluaga critics say Uribe will rule behind the scenes
By Helen Murphy and Brian Ellsworth
BOGOTA, May 26 (Reuters) - Colombian President Juan Manuel Santos' re-election bid took a hefty blow in voting on Sunday as his right-wing opponent won more support after attacking the government's peace talks with Marxist rebels.
Oscar Ivan Zuluaga, a former finance minister, won 29.3 percent of the vote in the first round of voting with Santos trailing on 25.7 percent.
The two men now go into a runoff on June 15 and will spend the next three weeks scrambling to win over voters who backed the three candidates eliminated from the race on Sunday.
Zuluaga has run an aggressive campaign, saying Santos' peace talks with the Revolutionary Armed Forces of Colombia (FARC) will damage national security and allow guerrilla leaders to escape prison sentences for war crimes.
Santos, a 62-year-old center-rightist, staked his presidency on the peace talks, saying they offer the best hope of finally ending a 50-year war that has killed 200,000 people.
For months, he had a comfortable lead in polls but Zuluaga surged in the last three weeks, backed by popular former President Alvaro Uribe, who turned against Santos over his decision to negotiate with the FARC.
Santos congratulated Zuluaga for his strong showing on Sunday but said the country needs to push for peace.
"We will now choose between the past and the future, we will choose between fear and hope, between those who deny peace and those who are ready to look for it," he told supporters in Bogota.
Santos will now seek the backing of losing candidates. Both Clara Lopez and Enrique Penalosa support negotiations with the FARC and they won a combined 23.5 percent of the vote on Sunday.
Against that, third-placed candidate Marta Lucia Ramirez is skeptical of the talks and many of her supporters are likely to swing behind Zuluaga. She won 15.5 percent support.
While many voters care more about the economy than the war, there is not much difference between the pro-business policies of Santos and Zuluaga. The most controversial issue was peace so the election became a referendum on Santos' strategy.
Zuluaga, 55, accuses Santos of giving too much away at the secret negotiations in Cuba, and has called for a return to the hardline military strategy that Uribe pursued during his eight years in power.
"We will decide on June 15 if we want more of the same or change for a better Colombia, if we want a country that gets more dangerous every day or if we want to build a safe country like the one we had between 2002 and 2010," Zuluaga told supporters on Sunday as confetti rained down.
He has vowed to give the rebels eight days to lay down their weapons and suspend negotiations if they refuse. That approach appeals to those Colombians outraged that FARC leaders could be spared prison time and allowed to run for Congress under a peace deal.
A regional breakdown of votes on Sunday showed strong support for Santos in areas of continuing conflict while Zuluaga won in areas that benefited from Uribe's U.S.-backed military offensives.
Ironically, Santos was Uribe's defense minister and took a share of the credit for capturing or killing rebel leaders and weakening the FARC's military capabilities.
The two men fell out when Santos opted to open talks with the rebels instead of sticking to Uribe's strategy.
Critics of Zuluaga say he is Uribe's puppet and would allow the former president to rule from behind the scenes. (Additional reporting Julia Symmes Cobb, Nelson Bocanegra and Peter Murphy; Editing by Kieran Murray)
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