WASHINGTON — The government opened its case in the trial of a top Latin American rebel leader, asserting yesterday that Ricardo Palmera joined a plot to take three Americans hostage after their American plane crashed in Colombia.

With tearful family members of the hostages sitting nearby, Justice Department attorney John Crabb argued that Palmera — better known by his nom de guerre Simon Trinidad — and his FARC leftist group sought to use the Americans as bargaining chips to extract concessions from the Americanbacked Colombian government.

“We’ll trade you hostages — including three Americans — for all FARC prisoners in jail. That was Simon Trinidad’s offer,” Mr. Crabb said.

“He admitted he was a member of FARC, he admitted FARC takes hostages,” he said. “That man Simon Trinidad tried to use them as get out of jail cards for FARC.”

Mr. Palmera’s defense countered that there was little evidence tying Mr. Palmera directly to the hostage-taking after the plane carrying the American military contractors encountered engine trouble in 2003 and crashed.

“This man had nothing to do with the capture of the three Americans,” attorney Robert Tucker, gesturing over to a subdued Mr. Palmera, said. “There’s no evidence he’s ever seen them.There’s no evidence he ever made any demand or talked to anybody.”

Chief U.S. District Judge Thomas Hogan swore in a panel of 15 jurors and alternates in the case of Mr. Palmera, who is considered the most senior member captured from the Revolutionary Armed Forces of Colombia (FARC).

The jury will decide the fate of Mr. Palmera in a 3-year-old kidnapping case in which the three Americans are believed to be held by guerrillas in the thick jungles of southeastern Colombia.

Mr. Palmera, 56, was extradited in late 2004 after his capture in Ecuador. He is charged with providing material support to a terrorist group and hostage-taking in connection with the February 2003 downing of a small American airplane over a FARC stronghold.

Upon entering the courtroom yesterday, Mr. Palmera, dressed neatly in a dark suit and green tie, flashed a smile to the packed courtroom audience. He quietly sat next to his attorneys, using headphones to listen to a Spanish translator.

FARC is demanding that the Colombian government release all of the group’s imprisoned comrades, including Mr. Palmera, in exchange for the release of 62 hostages.The hostages include the three Americans on the plane — Thomas Howes, Keith Stansell, and Marc Gonsalves — who authorities say were defense contractors involved in an intelligence-collecting mission.Mr. Palmera is also charged in the killings of two others on the plane, American pilot Thomas Janis and Sergeant Luis Alcides Cruz, a Colombian soldier, who were found near the crash site apparently shot to death.

The trial is the latest evidence of a toughened American stance against FARC, which the American government considers a terrorist organization. Since 2000,America has given more than $4 billion to Colombia to fight the insurgency and the world’s largest cocaine industry.

If convicted, Mr. Palmera could face 30 years in prison, the maximum allowed under the extradition treaty between Colombia and America. Family members of the hostages say they welcome Mr. Palmera’s trial, although they acknowledge it could backfire. The three hostages are believed to be alive but haven’t been publicly seen since a July 2003 video released by the rebels.