PANAMA -- One of the four Cuban exiles arrested in Panama last year in connection with an alleged plot to kill Fidel Castro told investigators in an ``informal conversation'' that he planned to assassinate the Cuban leader with a car bomb but changed his mind at the last minute, Panamanian authorities say.

In a series of interviews with The Herald this week, the officials also offered the most complete account yet of the events leading up to the arrest of four alleged conspirators last November -- including a disclosure that Castro himself personally delivered a key piece of information to Panamanian investigators.

According to the officials, 70-year-old Luis Posada Carriles, a veteran of countless previous anti-Castro conspiracies, told investigators that he called off the plan to kill Castro during a Latin American summit in Panama because too many innocent people would have been harmed as well.

Posada Carriles and three Miami men are in jail here on charges of illegal possession of explosives and conspiracy.

However, Panamanian officials -- who spoke on condition that they not be identified -- admitted their case against the men is extremely weak and predicted that they will be acquitted at trial.

NO EXTRADITION

Extradition of the men to Cuba, which Castro has demanded, has been flatly ruled out at the highest levels of the Panamanian government, the officials said. In addition to Posada Carriles, the others are Gaspar Jiménez, 65; Pedro Remón, 56; and Guillermo Novo, 61.

The four were arrested Nov. 17 during the Ibero-American Summit, after Castro warned Panamanian security forces that Posada Carriles was in Panama City to assassinate him.

According to the version of events provided by Panamanian officials, the Cubans brought as many as 100 security agents to Panama to prepare for the summit; some of them were under cover as teachers and businessmen.

But the Cuban government
never offered any evidence that Posada Carriles was in Panama until Castro himself was passing through the reception line at Panama City's Tocumen International Airport Nov. 17.

As he shook hands with Panamanian officials, Castro said he needed to meet with them at his hotel -- ``I've brought some information from Havana for you.''

CASTRO'S NEWS

About half an hour later, at the hotel, Castro told the Panamanians that Posada Carriles had entered Panama earlier in the month and was staying at a Panama City hotel under an assumed name. The Panamanian officials immediately dispatched a team of policemen to the hotel.

But what they did not know was that, immediately after meeting with them, Castro gave a press conference at which he revealed Posada Carriles' presence to the entire world.

``If any of those four guys had been watching television, they would have gotten away,'' said one Panamanian official.

Instead, two of the men -- Novo and Remón -- were arrested in the street outside the hotel when they tried to run after spotting the police. Posada Carriles and Jiménez were arrested upstairs in their hotel rooms, where they had just awoken from naps.

GROUNDS FOR BELIEF

``That's why I'm inclined to believe Posada Carriles when he says the plot had been called off,'' said a Panamanian official.

``He wasn't acting like a guy who was stalking Castro. Instead of watching TV, trying to figure out Castro's plans, he was sleeping. That doesn't sound like an active assassination plot to me.''

The three Miami men continue to insist that they came to Panama merely to protest Castro's visit, authorities say. But Posada Carriles, in informal conversations, has admitted that he was here to kill Castro, according to the same sources.

They said he told them the plan was to pack an automobile with plastic explosives and then detonate it as Castro's motorcade passed. But he decided that too many other people would be killed, the authorities said, and decided to drop the idea.

Because Posada Carriles talked about the plan but would not provide a sworn statement to investigators, however, his declarations cannot be used as evidence.

And, the Panamanian officials admitted, the links between the accused plotters and the only significant physical evidence in the case -- a briefcase full of plastic explosives found in a rental car they were using -- are too weak to win a conviction.