By JUAN FORERO
 
BOGOTÁ, Colombia, April 21 — Days after an assassination attempt on Carlos Castaño, the driving force of Colombia's right-wing paramilitary army, his disappearance has thrown peace talks between the paramilitaries and the government into a state of turmoil. It has also threatened a cornerstone of President Álvaro Uribe's strategy to pacify the country.

Mr. Castaño, a founder of an antiguerrilla movement known for mass killings and drug trafficking and classified as a terrorist organization by the State Department, was the target of an assassination attempt on Friday by a rival faction of the organization. It remained unclear on Wednesday if Mr. Castaño had been killed and his body hidden or if he had escaped into the jungle.

The government, concerned about how the internal divisions in the group would affect negotiations, sent Mr. Uribe's peace negotiator, Luis Carlos Restrepo, on Wednesday to meet with paramilitary commanders to determine what took place. "We are hoping for information so we can analyze what can happen to the process," said Ricardo Galan, a spokesman for the presidency.

Though considered a warlord responsible for hundreds of deaths, Mr. Castaño had led paramilitary leaders in disarmament negotiations that are crucial if the government is to remove one of three insurgencies from Colombia's 40-year conflict. The United States has been a firm supporter. But Mr. Castaño's candid style — in 2001 he authorized a biography, "My Confession," in which he brazenly admitted planning massacres and assassinations — has angered other commanders in the organization, who had come to view him as a liability.

Indeed, Mr. Castaño had accused other commanders of being more interested in cocaine trafficking than in fighting Marxist rebels. Mr. Castaño had denied being a drug lord, though he and two other commanders were indicted in the United States on trafficking charges.

"I think he has become expendable," Mr. Castaño's lawyer, Joaquín Peréz, said by phone from Miami. "I think he was driven by some degree of idealism. I believe the others did not share that idealism."

Mr. Castaño, a wiry man whose raspy, gruff voice is well known from television, founded the United Self-Defense Forces of Colombia with his brother, Fidel, after their father was kidnapped and killed by Marxist rebels in the early 1980's.

A confederation of regional factions with as many as 15,000 fighters, the group eroded support for rebels by killing hundreds of Colombians. Its money has come from ranchers, wealthy Colombians and, the United States says, drug trafficking.

Rodrigo Franco, a paramilitary commander who has known Mr. Castaño well, said he might have been killed by the most powerful drug trafficker in the organization, Diego Fernando Murillo. "The assassination and possible death of Carlos is the result of the reunification of the narcos," Mr. Franco, who leads a renegade wing in the group, wrote in an e-mail message.

His rivals in the organization worried that Mr. Castaño would surrender to the United States, as he has threatened in the past, providing the Bush administration with invaluable information about the paramilitaries in drug trafficking.

In Bogotá, officials expressed concern about the future of seven-month-old negotiations aimed at demobilizing the group by 2006.

"What happened to him demonstrates the two tendencies in the group, one open to dialogue and one that does not want to negotiate," said Senator Samuel Moreno, a member of the Colombian Senate's peace commission.

Mr. Moreno added, "This is a very big blow to the peace process."

Those negotiations have already been rocky, since paramilitary commanders have demanded that they not be jailed or extradited to the United States in return for disarming. Though the Uribe administration has given some signs that it is open to being more flexible on extradition, the disappearance of Mr. Castao has presented another obstacle.

Bishop Julio César Vidal, a Roman Catholic who is taking part in the talks, said the paramilitaries had to explain what had occurred. "We work in an environment of clarity and truth," he was quoted as saying in El Tiempo. "When we do not find those conditions, we have nothing to do with it."

Francisco Santos, the vice president, told reporters on Wednesday: "Without a doubt, they have to clarify to the government what happened. That means Mr. Castaño needs to turns up alive or dead."

Another paramilitary commander whose relationship with Mr. Castaño had been strained, Salvatore Mancuso, told El Colombiano of Medellín that there was no assassination attempt but rather a gunfight between paramilitary fighters and Colombian troops. He suggested that Mr. Castaño used the gunfight as a smoke screen to fade away and surrender to American authorities.

United States officials, though, have denied having any contact with Mr. Castaño, or knowing where he is.

Mr. Franco, the paramilitary commander, said he was told that three carloads of paramilitary gunmen arrived last Friday at a ranch in northern Colombia where Mr. Castaño was staying and opened fire. Seven bodyguards were killed, Mr. Franco said, and Mr. Castaño made his escape with three others. It was unclear, Mr. Franco said, if Mr. Castaño was able to later elude his assassins or if he was killed.

Mr. Franco, who is at war with the traffickers in the paramilitary organization, said that the shooting demonstrated that the Self-Defense Forces have become "an armed drug-trafficking cartel and the only thing that keeps them united is the fight against extradition and trying to resolve their legal problems and those of their supporters."