BOGOTA (Reuters) - Colombia could hold a public vote to approve a peace accord with Marxist FARC rebels and end more than five decades of war before the deal is formally signed, President Juan Manuel Santos said on Thursday.

It had been widely expected the plebiscite would take place after the government and the Revolutionary Armed Forces of Colombia (FARC) had officially signed an accord at the close of negotiations in Cuba.

"When we finish the agenda points, that is to say, when everything is agreed, that is when we will send the texts to Congress and convene the plebiscite," Santos said during an event in the Pacific port city of Buenaventura.

"That moment won't necessarily coincide with the signing of the accords. The signing is a formality, it can be done afterward," the president added.

The constitutional court ruled last month that a plebiscite could be held to legitimize any deal and that at least 13 percent of the electorate, some 4.5 million voters, would need to vote 'yes' for it to be approved.

The country's principal opposition party, the right-wing Centro Democratico, said this week it would campaign for a 'no' vote.

The government and FARC have been hammering out accords in Havana since 2012 on agricultural reform, FARC participation in politics and dismantling the illegal drugs trade, as well as other agreements Santos hopes will allow the rebels to hand in their weapons.

(Reporting by Monica Garcia; Writing by Julia Symmes Cobb; Editing by David Gregorio)