Fidel Castro's suggestion that an epidemic fever now sweeping his island could have been unleashed on Cuba by the United States may signal the end of his recent efforts at rapprochement with Washington.
Those efforts clearly have not met with much success for Cuba -- either with President Carter or with President Reagan.
High Cuban officials here indicate a sense of frustration with Washington, arguing that the US in the past year or so has rejected or ignored a variety of Cuban overtures toward improved relations.
There is a feeling in some foreign diplomatic circles here that Cuba's economic setbacks at the end of the 1970s prompted the overtures in the first place. But now with an improving economic picture, this reasoning goes, there is less pressure on Dr. Castro to seek an accommodation with Washington, which presumably would have benefited Cuba economically.
Whatever lies behind the apparent switch in Cuban tactics, there is no mistaking Dr. Castro's impassioned attack on the US -- which to many here was reminiscent of Castro's speeches of the 1960s.
Speaking July 26 on the 28th anniversary of his revolutionary movement, the Cuban leader recited a litany of charges of US preparations for biological and chemical warfare. Then near the end of his two-hour speech he implied the US may be involved in Cuba's wave in dengue fever.
Ignoring the fact that dengue fever has been sweeping much of the Caribbean, Dr. Castro suggested that mosquitoes that are said to bring the fever "could have been put in Cuba by the CIA."
While Castro indicated he still would like to explore rapprochement, observers suggest those words were aimed most directly at his domestic audience.
Dr. Castro took a number of other swipes at the U.S. He noted Cuba's recent capture of Cuban exiles who had slipped into the island in what the Miami-based exile organization Alpha 66 claimed was an effort to kill him.
Diclosing that five mercenaries had been picked up in early July, he asked why the US has not said "a single word" about it. "Washington has said absolutely nothing," he said, adding, "It is an ominous silence."
Dr. Castro also cited actions by Washington that he said were aimed at hurting the Cuban economy -- actions such as keeping Western firms from purchasing Cuban nickel and encouraging Western banks to refuse loans to Cuba. He also cited "sinister reports" of trouble in Cuba's sugar-cane fields and a poor 1981 harvest.
The Castro speech was a firm refutation of allegation that Cuba's economy continues to falter.
Dr. Castro claimed important economic advances during the past year, and most particularly during the last six months. The sugar harvest was excellent at almost 8 million tons. The tobacco harvest, after two years of a crop disease that brought production to a standstill, was 50,000 tons -- "one of the best in history," he noted.
AS he ticked off the statistics, it was evident that an across-the-board 20 percent increase in production touched most of the agricultural crops and many industrial products as well.
At the same time, Dr. Castro admitted that the laying of railroad tracks and the improvement of rail services on the island is way off schedule, that a serious drought has cut the important rice crop, and that there are other slippages as well.
The overall picture, however, is a favorable one for Castro and his revolution. Independent observers in Havana confirm this good report card.
But it was the verbal attack on the US and the implication of a possible US role in the current dengue fever epidemic that drew attention in Cuba. There was strong feeling that the Castro remarks are a clear statement that Cuba is changing course and that Dr. Castro does not expect that an improvement in relations with Washington is possible with Ronald Reagan in the White House. Well-placed Cuban officials tend to confirm this assessment in private conversations. The Castro speech, delivered in the Cuban province of Las Tunas. Was broadcast and telecast throughout the island and beamed overseass on Cuban shortware.