Secretary of State John F. Kerry listens as Bernard Aronson speaks to reporters at the State Department in February, when Kerry announced that Aronson would be the new special envoy for the Colombian peace process. (Pablo Martinez Monsivais/AP)

At his first meeting with Colombia’s Revolutionary Armed Forces in February, Bernard Aronson began with a joke. “Maybe you were expecting Miss Universe?” he asked, referring to the Colombian winner of the international beauty contest just a few weeks before.

“Well, you’ll have to settle for me,” Aronson told the six guerrilla representatives gathered around a diplomat’s swimming pool in Havana. They laughed, he laughed and the ice was broken.

Since then, Aronson has met regularly with representatives of the FARC — the group’s Spanish acronym — as the Obama administration’s special envoy to peace negotiations between the guerrillas and the Colombian government. He is due to return to Cuba, after testimony at a House hearing, this week.

It is a strange role for the representative of a country that has designated the FARC an international terrorist organization and that has spent billions over the past two decades supporting Colombia’s war against it. A number of senior FARC leaders were extradited to this country and are now serving sentences for drug trafficking, murder and other crimes; dozens are the subject of outstanding extradition requests, some of them reportedly among the Havana negotiators.

But the moment, and the man, seemed right. By early this year, the negotiations that began in Cuba in 2012 had made notable but slow progress. Colombian President Juan Manuel Santos, after his reelection, personally asked Secretary of State John F. Kerry to lend a hand, and the FARC, surprisingly, thought it was a good idea. President Obama’s diplomatic opening to Cuba, announced in December, made it possible to send an envoy for extended stays on the island.

Within weeks of his February appointment, Aronson was sitting with the guerrillas in Havana — the FARC’s first known contact with a U.S. official since a then-
secret 1998 meeting to discuss kidnapped American missionaries.

The FARC has publicly called on the United States to end extradition from Colombia and to release its leaders — especially Ricardo Palmera, the guerrilla commander best known by his nom de guerre, Simón Trinidad. Extradited in 2004, Trinidad is serving a 60-year sentence in a supermax prison in Colorado for conspiracy related to three American defense contractors being held hostage for five years, ending in 2008.

FARC negotiators have said the peace talks would be facilitated if Trinidad were there to participate, and even Santos said recently that he didn’t believe that “any guerrilla is going to turn in his weapon only to go and die in a U.S. jail.”

Aronson said that the subject of Trinidad has not been discussed with the FARC and that “from the point of view of the United States, extradition is not on the table.”

The envoy does not participate directly in the negotiations. Cuba and Norway, whose Havana ambassador has lent his poolside ­patio for U.S.-FARC meetings, are the official “facilitators” of the talks. There have been 38 negotiating sessions over the years.

Instead, Aronson’s separate meetings with the two delegations can help “oil the gears” by interpreting each side to the other and keeping demands within the realm of the realistic, he said.

More important, he can reassure them that the United States, having funded one side of the war, is prepared to help fund the peace for both, and “to say to the FARC” that the United States “is not automatically hostile to left-leaning ­regimes in the hemisphere,” Aronson said in an interview.

“Once you give up armed struggle, rejoin society and meet your legal obligations, the United States is going to be supportive of the implementation, just as we have been in other post-conflict settlements,” he said.

Aronson, now in the private sector, played a similar role as president George H.W. Bush’s chief diplomat for Latin America in helping to negotiate and guarantee U.S. support for peace deals that ended Central America’s wars in the late 1980s.

Considerable help will be needed to end what is now the world’s longest ongoing guerrilla war, a conflict that has taken more than 200,000 lives in Colombia.

A shaky cease-fire that had prevailed for months broke down in April, when a FARC unit opened fire on a military patrol, killing 11 soldiers. Government retaliation has left dozens of guerrilla fighters dead, and subsequent FARC attacks on Colombia’s infrastructure have left hundreds of thousands without electricity.

For many Colombians, the renewal of violence has significantly damaged confidence in the negotiating process. A Gallup poll in April indicated that support for the peace talks had fallen to 29 percent from 43 percent just two months earlier. Support for a military victory against the guerrillas rose from 25 percent to 42 percent.

Continued fighting is also likely to undercut the administration’s ability to persuade Congress to continue to fund a Colombia aid budget that is already in decline.

Despite the upheaval, there has been some progress on the ground. The government announced it would stop a U.S.-backed aerial fumigation program targeting coca, the main ingredient of cocaine, and Colombian soldiers and FARC guerrillas have participated in a pilot program to begin clearing land mines in a small town in the northern part of the country.

In Havana, the talks have continued. Over the past two years, agreements have been reached in several of the main areas of negotiations — including land reform and, most recently, the establishment of a truth commission, charged with “clarifying and making known the truth about what happened in the conflict.”

But the hardest parts are still ahead — how to demobilize and disarm the guerrillas and who, if anyone, has legal responsibility for events during a half-century of killing on both sides.