By ANDY ROSENBLATT

Three Cuban nationals, suspected of spying for the Castro government, were arrested at Fort Lauderdale-Hollywood International Airport Friday carrying Nicaraguan passports and preparing to board a Nicaraguan-registered jet.

The three men, identified by the FBI as employees of Cubana Airlines, the official airline of Cuba, were charged at the direction of FBI counterintelligence agents with violating U.S. immigration laws.

The trio's sleek orange-and-white Lear jet was seized at a private airplane hangar in Fort Lauderdale until FBI agents can determine if the aircraft is, as they suspect, owned by the Cuban government.

The agents expect to obtain court permission to search the plane today.

The three men - Simon Delfin Espinosa Alvarez, 36; Luis Leonardo Herrera Altuna, 34; and Jorge Hermenegildo Toledo Infante, 35 -were transported to Dade County Jail and ordered held on separate $500,000 bonds.

An unidentified fourth man who accompanied the Cubans was questioned but not arrested.

The three Cubans, all pilots, have entered the U.S. at least three times since obtaining tourist visas through the U.S. Embassy in Managua, Nicaragua.

They were able to obtain the visas after presenting U.S. Embassy officials with passports issued by the Nicaraguan Ministry of Interior on Feb. 5.

Only Nicaraguan citizens are legally eligible for Nicaraguan passports.

U.S. Officials here already have asked Nicaraguan Consul General Mario Gonzalez to explain how the Cubans were able to get Nicaraguan Passports. Gonzalez did not return The Herald's calls Friday night.

According to their passports, the trio has made several trips to the United States, entering the country at different locations, since June 21.

FBI Special Agent in Charge Arthur F. Nehrbass refused to say where the three Cubans were headed as they prepared to board their jet Friday afternoon. Other individuals said they were apparently planning to fly to another destination within the U.S.

But a Federal Aviation Administration official said that the Cubans actually took off from Fort Lauderdale Thursday en route to Managua but developed engine troubles and returned to the Broward County airport for repairs.

An employee of Graf Jets, a private airplane hanger in Fort Lauderdale, called the Cubans "regular customers."

He did not elaborate.

At an evening press conference, Nehrbass tried to avoid specifically identifying the three men as Cuban intelligence agents or discussing what they were doing here.

He did say that the Cubans were arrested "as a result of information we developed as an outgrowth of investigations into Cuban intelligence matters."

Nehrbass emphasized that the Cubans were carrying passports issued by the Sandinista-controlled Nicaraguan government, which seized control of that Central American nation last year.

U.S. officials believe that Cuban intelligence agencies have, for years, maintained a continuing interest in obtaining military secrets here and monitoring the activities of the Cuban exile community.