BY GLENN GARVIN

 PANAMA -- Police found a large sum of cash, tens of thousands of dollars, in the
 hotel rooms of four Cuban exiles arrested here last week in connection with a
 supposed plot to kill Cuban President Fidel Castro.

 Sources familiar with the investigation said the men claimed the money was to
 buy advertising on Panamanian radio and television stations denouncing Castro's
 visit to Panama last weekend.

 The four exiles -- Luis Posada Carriles and Miami residents Gaspar Jiménez,
 Pedro Remón and Guillermo Novo, all veterans of numerous anti-Castro plots --
 were arrested Friday after the Cuban leader accused them of planning to
 assassinate him during last weekend's Ibero-American summit here.

 None of the men have been charged. But the Cuban government has asked for
 their extradition to face charges there stemming from their decades-long war on
 Castro.

 No weapons were found when the men were arrested. But police believe they are
 connected to 18 pounds of plastic explosives discovered Sunday near Panama
 City's international airport. Two Panamanian residents -- Cuban-born
 businessman César Matamoros and chauffeur and José Hurtado -- have also been
 arrested in connection with the alleged plot.

 Sources close to the investigation say the two men have admitted knowing the
 four exiles, but denied being part of any plot.

 The two Panamanian residents "say Posada Carriles came to them and wanted
 to buy a water pump to take back to his home in El Salvador,'' a source said.
 "But they say they never heard any talk about killing Castro.''