The State Department, sharply rebutting an accusation by Cuban President Fidel Castro that the Central Intelligence Agency caused a virus epidemic in his country, disclosed this week that the administration will permit Cuba to buy a pesticide to control the disease.

In a rambling speech Sunday, Castro charged that the CIA was behind a recent outbreak of dengue fever, an infectious tropical disease transmitted by mosquitoes, that has killed 113 Cubans and infected nearly 300,000 others.

Castro also charged that the CIA was behind several agricultural infestations that have damaged Cuba's tobacco and sugar crops recently.

"The Cuban revolution is a failure and it is obviously easier to blame external forces like the United States than admit the failures," State Department spokesman Dean Fischer said.

Dengue fever normally causes extreme pain and stiffness in joints. But the viral strain now causing the epidemic in Cuba is a more serious form that causes hemorrhaging, tropical specialists said.

They said the more deadly form was brought to Cuba by soldiers returning from Angola, where a Cuban expeditionary force has been deployed since late 1975.

Fischer said the administration granted an export license 10 days ago for about 660,000 pounds of Abate, a U.S.-manufactured pesticide to kill mosquitoes that spread dengue fever.

The request for the license, which is necessary to circumvent a long-standing U.S. embargo on trade with Cuba, was made by the Pan American Health Organization July 17. Officials approved the license that day, but the shipment has not been sent.

The Cubans are to reimburse the health organization for the $330,000 cost of the pesticide.

There has been no mention of the U.S. origin of the pesticide in Cuba's official press, and Castro's exploitation of the issue was seen as a "cheap and cynical trick," in the words of one official who did not want to be identified.