After nearly four decades of Cold War with Cuba, the FBI said Monday that it broke up the biggest spy ring in years from the communist island, alleging that a dozen operatives sought to infiltrate U.S. military bases in South Florida and sow discord among exile groups in Miami.

Since the early 1990s, prosecutors said, a spy cell whose members lived in Broward, Miami-Dade and Monroe counties quietly targeted MacDill Air Force Base in Tampa, the U.S. Naval Air Station at Boca Chica near Key West and, more recently, the U.S. Southern Command. Southcom, in West Dade, oversees American military activities in Latin America and the Caribbean Basin.

``In scope and in depth . . . it is really unparalleled in recent years,'' U.S. Attorney Thomas Scott said at a jammed news conference at FBI headquarters. ``This spy ring was sent by the Cuban government to strike at the very heart of our national security system and our very democratic process.''

Investigators said it was the first time in memory that a Cuba-sponsored spy ring had been dismantled in South Florida, even though between 200 and 300 operatives are believed to have worked with impunity in the Miami area for decades.

Neither prosecutors nor investigators would say how they came to identify the ring or what Cuba planned to do with any intelligence its alleged spies may have gathered.

The government's allegations, disclosed in a 20-page criminal complaint filed Monday in U.S. District Court in Miami, are the broadest and most detailed outline of alleged Cuba-sponsored espionage activities in the United States, investigators said. Ten suspects were arrested at their homes over the weekend; two others had left the country.

Those arrested have been charged with conspiracy, working as unregistered agents for a foreign power, and seeking to deliver American defense information to a foreign power -- the Cuban government. At least two of the suspects are U.S. citizens.

Some of the suspects face possible life terms in prison if convicted. Others face up to 15 years.

``The group, through its lead agents, communicate directly with the government of Cuba about their activities and receive specific missions and assignments from the Cuban government,'' FBI agent Raul Fernandez wrote in the criminal complaint.

Scott said the members employed code names, hatched escape plans and even held ``escape alibis'' to avoid capture and detection.

Items confiscated

Members of the FBI's counterintelligence office in North Dade rounded up the majority of the alleged ring in raids on homes from Hollywood to Big Pine Key. Agents confiscated portable computers, shortwave radios, cell phones, floppy diskettes and documents such as blank pilot flight logs and a job application for the U.S. Naval Air Station at Boca Chica.

The Cuban government said it knew nothing about the arrests.

``We only know what has been said on the wires,'' Foreign Ministry spokesman Alejandro Gonzalez told the Spanish news agency EFE. ``This is a matter in which the American authorities are involved, and we don't feel it is responsible of us to comment on a matter we don't know anything about.''

U.S. authorities said agents chose to arrest the group because some members were planning to return to Cuba. In Miami, the FBI said only that the time was right to shut down their activities.

The arrests come at a time when congressional representatives from South Florida have expressed concerns about heightened travel by Cuban officials to Florida and New York, and the recent indictment of Cuban exiles in Puerto Rico for allegedly plotting the assassination of Cuban President Fidel Castro. Some exiles have charged that the federal government has been setting the stage for easing the embargo against the island.

The U.S. motive

But the State Department adamantly denied that the vagaries of exile politics played a part in the arrests.

``These arrests show that the United States will not tolerate any attempt by any government to take advantage of our open democratic system,'' spokeswoman Lula Rodriguez said.

She said the department wants to emphasize that the roundup was the result of an ``independent'' law enforcement investigation designed to protect U.S. security interests.

One congressional staff member familiar with intelligence matters said Cuba shares information it gathers with such nations as Russia, North Korea, China and various Middle East adversaries of the United States. He said the FBI considers Cuban intelligence to be the No. 2 agency behind the Russians in terms of ``adversary intelligence agencies.''

In Miami, Cuban-American politicians have long feared and suspected that Castro operatives are living among the exiles who fled his regime.

Juan Cortinas, a spokesman for Rep. Ileana Ros-Lehtinen, said the Miami congresswoman met with U.S. intelligence authorities in July and asked them to investigate travel by Cuban officials to Miami because they might be trying to penetrate exile groups.

``Last year we reached an agreement with the State Department that every time a Cuban official would come here, we need to see the paper of where they are going,'' Cortinas said.

Cuban intent assessed

Rep. Lincoln Diaz-Balart, also of Miami, called the arrests an indicator that Cuba remains a ``terrorist state.''

The Cuban American National Foundation said the arrests offer a ``rude awakening to those who have argued that Cuba no longer presents a threat to the U.S.''

``For the tyrant, the Cold War remains very much alive, and the only change necessary is to strengthen U.S. resolve and respond to this flagrant act of aggression in the strongest manner possible,'' said foundation Chairman Alberto Hernandez.

In court Monday, the alleged agents -- eight expressionless men and two women -- did not seem to fit the role. Appearing in blue prison garb before U.S. Magistrate Barry Garber in a packed Miami courtroom, most were assigned defense attorneys at U.S. taxpayers' expense. A majority said they lacked the money to pay lawyers. None had more than $2,000 in the bank. They drove old cars, lived in cheap apartments.

The government said there were actually a dozen people associated with the ring. But two suspects, identified as Ricardo Villarreal and Remijo Luna, apparently got away. ``Both men have since left the United States for other operational assignments,'' the affidavit says.

Brothers to the Rescue leader Jose Basulto appeared both in federal court and outside FBI headquarters, where he and an assistant were refused admittance to the news conference.

``This is just the tip of the iceberg,'' Basulto said. He branded the suspects ``cheap Cuban spies.''

Brothers to the Rescue lost four of its members in 1996 to Cuban Air Force MiG jet fighters, which shot down two propeller-driven planes near Cuban waters. The shootdown provoked an international incident, heightened tension between Washington and Havana, and inspired Congress to tighten the longstanding economic embargo against the island.

In the midst of the diplomatic furor, the exile community was shocked when Juan Pablo Roque, a Brothers pilot, suddenly dropped out of sight and reappeared in Havana, proclaiming himself a double agent who worked for Castro.

Scott and the FBI refused to discuss any possible relationship between Roque and the case against the arrested spy suspects.

Basulto said that after he reviewed the day's events, he would have more to say at his own news conference today.

Under surveillance

Since 1995, the FBI has watched the accused operatives, obtaining warrants to monitor their telephone conversations between Florida and Cuba.

A pivotal leader was said to be Manuel Viramontes, a Cuban military captain who used computers to communicate with other alleged cell members from his apartment in North Miami Beach. When speaking by phone with his subordinates, the FBI affidavit said, he employed a bogus Puerto Rican accent. Even his name was phony, the document said. Diskettes seized at his home offered investigators a road map of the ring's activities, they said -- right down to references of his associates as ``comrades.''

Other top associates included Ruben Campa and Luis Medina, as well as Villarreal and Luna. Medina is said to have received reports from fellow agents on Southcom and Boca Chica.

At one point in July, agents overheard Campa and Viramontes discussing a mutual acquaintance who had encountered trouble in Moscow.

Another member, Rene Gonzalez, once affiliated himself with Brothers to the Rescue, and more recently with the Democracy Movement, the government said.

Besides infiltrating exile groups, the alleged spies sought to gain employment at military bases such as the one at Boca Chica and at the Southern Command. One, Antonio Guerrero, worked as a civilian employee at Boca Chica. He was ordered to report ``unusual exercises, maneuvers, and other activity related to combat readiness'' at the Naval Air Station, the affidavit alleged.

There were also efforts to get other jobs. Among the evidence on display at FBI headquarters: a notice of an opening for a housing repairman at Boca Chica, at $14.04 an hour. But it appeared that no one else in the group worked at a government installation.

Herald staff writers Manny Garcia, Don Finefrock, Andres Oppenheimer and Juan Tamayo contributed to this report.