SAN JUAN, Puerto Rico -- Federal prosecutors in Puerto Rico are investigating a Miami bank account in the hope it will shed light on the funding of an alleged Cuban exile plan to assassinate President Fidel Castro, according to a source close to the case.

The account's holder, a 61-year-old Cuban exile named Juan Bautista Marquez, was arrested in Puerto Rico on Oct. 27 with three fellow exiles aboard the yacht La Esperanza.

U.S. Coast Guard agents found two .50-caliber rifles and a supply of ammunition hidden aboard the 46-foot boat, which is registered in Miami.

Marquez, a former merchant seaman who lives in Miami, opened a joint Citibank account with his brother Julian on July 27 with a $2,000 deposit. The next day, a $2,990 transfer came in from an unidentified account, court documents show.

Four withdrawals totaling $737 and one deposit of $127 were made between July 27 and Oct. 13, according to the last statement turned over to prosecutors by Citibank, leaving a balance of $4,363.38.

`No mystery'

Marquez's lawyer in Puerto Rico, Juan Massini, told The Herald that the account is in no way connected to the prosecutors' investigation of La Esperanza's voyage in October.

``There's no mystery there. That's a personal account that was opened long before the events transpired,'' Massini said.

According to Massini, his client received a $2,000 advance from a man named Otero for taking the boat out of a private dock in Miami in late October.

The lawyer said he wasn't sure whether his client deposited the advance in the Citibank account.

Otero was ``an acquaintance'' of his client, Massini said, adding that Marquez does not remember Otero's first name.

Awaiting trial

The prosecutor's office submitted a detailed rundown of the account to the federal court in San Juan, where the four exiles are awaiting trial on charges of illegal transport of firearms and making false statements.

The bank documents are also in the hands of a federal grand jury in San Juan that is investigating the testimony of one of the Coast Guard agents who helped intercept the exiles' boat off the southwest coast of Puerto Rico.

According to the agent, one of the exiles -- Angel Alfonso Aleman -- blurted out that the rifles would be used to assassinate Castro during the Ibero-American summit conference that was to be held Nov. 7-9 on the Venezuelan island of La Margarita. According to the agent, Alfonso, a 57-year-old Union City, N.J., businessman, said that the weapons were his and that his companions had no knowledge of the plan.

Hired to pilot boat

Marquez reportedly told the Coast Guard agents that he was unaware of the firearms on the boat, and claimed that he was hired to pilot the boat to St. Lucia in the Windward Islands, where it would be sold.

Castro's participation in the summit meeting on La Margarita proceeded as scheduled.

In December, the grand jury received documents from the FBI indicating that the rifles were purchased in Miami by two Cuban exiles -- Francisco ``Pepe'' Hernandez, president of the Cuban American National Foundation; and Juan Evelio Pou, a veteran of the 1961 Bay of Pigs invasion.

Other documents delivered to the grand jury identify Jose Antonio Llama, one of the foundation's 28 executive committee members, as the boat's owner. Hernandez appeared before the grand jury Nov. 19; Llama was also summoned to testify but his appearance was postponed and has not been rescheduled.

New charges expected

The exiles' trial was set for Feb. 27, but prosecutors have asked the judge for an additional 60 days to add new charges to the indictment and name new defendants. The new trial date has not been set.

In addition to Marquez and Alfonso, the defendants are Francisco Secundino Cordova, 50, a fisherman who lives in Marathon; and Angel Hernandez Rojo, 64, a Miami lumber dealer.

At a status hearing two weeks ago, Magistrate Justo Arenas scheduled a hearing for April 27 to rule on two motions made by Alfonso's attorney, Ricardo Pesquera, who asked the court to disregard the statements allegedly made by his client.