A Havana report accusing Cuban exiles in a string of bombings on the island has turned a spotlight on the long-running but little-known contacts between U.S. and Cuban counterterrorism agents.

Knowledgeable U.S. officials said the contacts have been taking place relatively frequently, two or three times a year, since the start of a spate of plots in 1991 by exiles animated by the collapse of the Soviet bloc.

Cuba's state security agencies complained to their U.S. counterparts after learning about many of the plots through the spies they are widely believed to have placed in most of the militant anti-Castro groups in Miami, the officials said.

Cuban President Fidel Castro confirmed the existence of such links when he told U.S. newspaper executives in Havana last week that his security agents had given the FBI and CIA information on alleged exile terrorists.

Castro spoke as he held up a report, apparently the same one that Havana made public Thursday, accusing the Cuban American National Foundation and one of its top officials of financing a string of terror bombings.

Havana's allegations were passed to the FBI several months ago and now form part of the background for a U.S. grand jury in Puerto Rico investigating several other reputed exile conspiracies, U.S. officials said.

But the topic of U.S.-Cuban security contacts is so sensitive on this side of the Florida Straights that none of the officials contacted by The Herald on the subject Friday would comment on the record.

Fears of betrayal

A concern heard Friday in Miami's Little Havana was that U.S. agents might betray exiles who could wind up before Cuban firing squads, or that innocent exiles could be prosecuted in the United States on phony charges from a communist dictatorship.

That's impossible, insist a half-dozen federal and local officials knowledgeable about the contacts and even a longtime Cuban ``spy who was in fact a double agent working for the FBI.

U.S. agencies never give information to Cuba that might lead to arrests, all the sources said, and the agencies use Havana's tips only to enforce U.S. neutrality laws, stop conspiracies in the United States and keep at least some exiles out of harm's way.

``Many Cubans in Miami probably owe their lives to the FBI people who broke up their plans against Cuba, said the former double agent, Francisco Avila, a onetime military commander of the Alpha 66 paramilitary group.

Under FBI orders to give Havana nothing of use, Avila said, ``I had to be an artist to give them reports with inoffensive information. Usually, nonsensitive stuff could be provided, but nothing that could make blood run.

`One-way relationship'

``It's a one-way relationship. They talk, we listen, said one American official who asked to be described only as ``having had access to some of the Cuban reports to us.

Havana and Washington have long been known to exchange information on illegal migration and drugs, although U.S. officials have been cautious on the drug side because of suspicions of corruption among Cuban government officials.

But the contacts between counterterrorism experts from such agencies as the FBI and CIA with their Cuban counterparts have been kept under the tightest of wraps because of their political sensitivity, officials said.

The officials said they were aware of such U.S.-Cuban contacts since the late 1980s, but that their number and importance grew after 1991, when many exiles came to believe that Castro had become vulnerable after losing his Soviet backing.

``The Cubans were in constant contact with reports of plots, demanding more and more action [crackdowns on exiles] but providing very little actual information, said one retired federal official.

Lack of detail

Pressed by Washington to provide details of its allegations, the official recalled, Cuba handed over a report in late 1992 or early 1993 ``that they could have gotten from news clippings and a few sources on the edges, the official said.

The lack of detail was apparently designed to protect the identity of Cuba's spies in Miami. But the report was enough to allow the FBI to warn the would-be plotters to stop whatever they were up to, the official said.

Cuba provided a far more detailed report around 1996 on an alleged exile plot to detonate a bomb near Castro as he delivered a speech in Havana's Plaza de la Revolucion, according to another knowledgeable official.

``The Cubans knew everything about the plot, so we sent some people to talk to some of the Miami exiles involved and the thing stopped in its tracks, the official said. ``We protected the exiles.

Some U.S. officials in fact were so concerned for exiles, said one federal source, that law enforcement agents dropped at least one case that could have sent an exile to a notorious jail in the Bahamas.

``We did cancel one case because we didn't want people rotting in Foxhill prison for something [a planned attack on Cuba] that probably never would have happened anyway, the official said.

Radio debate

Cuba's report Thursday on alleged exile terror bombings had some of Miami's Spanish-language radio programs debating Friday the propriety of the U.S.-Cuban counterterrorism contacts.

Several callers charged that the bilateral collaboration was part of a U.S. effort to silence exile hard-liners so that President Clinton could improve relations with Castro.

The Cuban American National Foundation pointedly stayed away from the debate, saying it agreed that the FBI had to investigate any information it received, even from Cuba.

``We understand the FBI is carrying out its duties, said CANF President Francisco ``Pepe Hernandez. ``But we do believe that these accusations . . . don't merit any credibility.

El Nuevo Herald staff writer Olance Nogueras contributed to this report.