By Helen Murphy and Luis Jaime Acosta
BOGOTA (Reuters) - Colombia's governing coalition emerged from elections on Sunday with its congressional majority intact but shrunken by the arrival of ex-president Alvaro Uribe's new party which opposes peace talks aimed at ending five decades of civil conflict.
The result consolidated President Juan Manuel Santos as front-runner in a presidential vote on May 25 but thins the majority he will rely on if re-elected, for legislative support to implement a peace deal with the Revolutionary Armed Forces of Colombia, or FARC rebels, if talks succeed.
Santos is seeking a second term to allow him time to complete negotiations with the FARC that could end a war that has killed around 220,000 and transform Colombia's political makeup if the rebels' gain the political participation they seek.
Uribe is a fierce critic of the government who believes the FARC should instead be beaten militarily. His party will likely seek to obstruct legislation if a peace deal is reached that would enable FARC rebels to enter the political system without serving considerable jail time.
With 95 percent of votes counted, 62-year-old Santos' center-right U Party emerged the single biggest party in both Congressional houses with 15 percent of the vote for each.
Including votes for coalition parties including the Conservative, Liberal, Green, Radical Change and U parties, the alliance held on to a majority of the 166 seats in the lower house and 102 in the Senate.
Uribe's Centro Democratico garnered almost 15 percent of votes in the Senate where the ex-president will take up a seat marking his return to political office after his mandate ended in 2010. The party won just under 10 percent of votes for the lower house.
The secretive peace talks reached a partial accord late last year on the FARC's participation in politics, a highly controversial item on the five-point agenda. Any deal with the rebels would be put to the nation in a referendum, and then to congress to devise laws for its implementation.
Despite slow but encouraging progress at the negotiations in Cuba's capital Havana that began in late 2012, the decision to engage in peace talks with the guerrillas remains divisive and will be pivotal in voters' choice of president in May.
URIBE FEARS FARC IMPUNITY
Some 32 million Colombians are eligible to vote, though congressional elections have a particularly high abstention rate and less than half that number turned up at polling stations in a vote that passed off in generally peaceful conditions.
Ex-president Uribe became the de facto opposition and Santos' fiercest critic shortly after backing him for office in 2010.
The two fell out when Santos mended ties with Venezuela's then-President Hugo Chavez, who had engaged in a diplomatic tussle with Uribe for years. The acrimony worsened when Santos announced peace talks with the FARC, seen as a terrorist group by the United Sates and the European Union.
"I'm afraid of what will happen if an impunity pact is signed with terrorist leaders," Uribe said at the close of his campaign. "When crime is a champion, there's no condition in the heart to forgive the criminal. The lack of justice may lead to peace accords in Havana but more violence in Colombia."
Colombia, a recipient of hundreds of millions of dollars in annual U.S. anti-narcotics aid, has fought the FARC, right-wing paramilitaries and a smaller rebel group, the ELN, since 1964. More than 200,000 people have died and millions have been displaced.
Santos is expected to reveal soon that the ELN will also start peace talks with his government, which is likely to give a further boost to his chances of securing another term.
Polls show Santos is likely to reach a second round of voting on June 15 with Oscar Ivan Zuluaga, the candidate for Uribe's party. The top two contenders go to a runoff if neither garners more than 50 percent of ballots cast in the first round.
Santos will also need backing in congress to pass reforms that would help bolster Colombia's $350 billion economy, create new jobs and cut the poverty rate, which affects about half the nation's population of 47 million.
(Additional reporting by Andres Rojas, Camilo Cohecha and Peter Murphy in Bogota; Editing by Daniel Wallis, Rosalind Russell and Eric Walsh)