(Recasts with poll details, FARC statement, byline)
By Peter Murphy
BOGOTA, June 6 (Reuters) - Three polls showed on Friday that Colombia's presidential race is too close to call as opposition challenger Ivan Oscar Zuluaga seeks to unseat President Juan Manuel Santos in a June 15 runoff focused on how to end the country's half-century guerilla war.
A Gallup poll showed the two candidates neck-and-neck, but two other surveys gave solid leads to one or the other.
The uncertainty intensifies the suspense in the final days of a bitter election battle in which Santos began as a comfortable favorite before Zuluaga surged with the backing of still-popular former president Alvaro Uribe.
Santos, 62, a U.S.-trained economist and scion of one of Colombia's most powerful families, has appealed to the electorate to give him another four-year mandate to complete peace negotiations he began with FARC rebels in 2012.
He is staking his reputation that the talks, being held in Cuba, will end the 50-year conflict in which 220,000 people have died.
Though Colombians are desperate for peace, Zuluaga, 55, who is also an economist, has been critical of the talks as being overly lenient on the Marxist rebels. He appeals to voters who believe the talks could lead to little or no punishment for guerrillas' war crimes and hand them instant political power.
Though Zuluaga has said he would continue talks, he would impose tougher conditions that could make the FARC walk away, leaving a return to the military option the only alternative.
The Gallup poll late on Thursday showed the candidates in a statistical dead heat, given the margin of error, with 48.5 percent for Zuluaga versus 47.7 percent for the president.
On Friday, a Cifras y Conceptos poll showed 43.4 percent of respondents would vote for Santos and 38.5 percent for Zuluaga, while research firm Ipsos Napoleon Franco gave 49 percent to Zuluaga and 41 percent to Santos.
REBEL LEADER SCOFFS
Only one of the surveys, Ipsos, was still being done on Wednesday this week, when Clara Lopez, a leftist candidate defeated in the first round of voting, publicly threw her support behind Santos.
She had around 15 percent of first round votes.
The election has been broadly portrayed, particularly by the Santos campaign, as a choice between war and peace, even as government troops keep fighting the rebels in their jungle strongholds while peace talks continue in Havana.
The presidential rivals are former cabinet colleagues under Uribe and both support free-market economics and continued close ties with the United States.
FARC leader Rodrigo Londono, known by his war alias as Timochenko, scoffed at both candidates in a lengthy statement this week, saying they are both warmongers.
"Colombians face a real dilemma," he said.
"But it's not that they must choose between war with Oscar Ivan Zuluaga and peace with Juan Manuel Santos. It's clear that either one of them represents war," he added, calling for a "powerful coalition" of the left to face whoever wins. (Additional reporting by Helen Murphy and Luis Jaime Acosta; Editing by Andrew Cawthorne and Peter Galloway)