By MERWIN SIGALE

Fidel Castro has raised the lid from a Pandora's box of problems plaguing his Communist revolution.

At a rally in Havana's Plaza of the Revolution Saturday night, out popped revelations of widespread sabotage, teenage prostitution, youth crime and defiance of authority, "fabulous rumors" about vampires and child kidnapings, and the first admitted desecration of Che Guevara's memory in Cuba.

Although the problems of prostitution and rebellious youth seemed concentrated in Havana, that was notably not the case with a wave of sabotage that has swept the island in the last six months.

Castro ticked off a list of 15 major acts of sabotage, 13 of them fires, since April 6. Only one was in the capital. But there were six in easternmost Oriente Province where his revolution was born and drew its greatest strength.

The Cuban premier charged that counterrevolutionaries also set fire this year to 36 small schoolhouses - 13 in Oriente, again more than one-third of the total. Twelve of the burned schools were in Havana Province, but it was not clear if any were in the capital itself.

Castro gave damage estimates for only five of the major sabotage cases, and they totaled $2.6 million. Items destroyed included buildings, fertilizers, hides, clothing, sacks of sugar and agricultural machinery. Warehouses were favorite targets. In only one case was a terrorist captured. The premier also reported 25 lesser acts of sabotage this year against stores, hotels, agricultural buildings, coffee trees and timber.

Castro promised tougher penalties for counterrevolutionary acts. "These are the rules of the game," he said. "Before they destroy this revolution, first the heads of all who want to destroy it will roll . . . The revolution will be severe, implacable and inflexible."

In Havana, where Castro has encountered the most resistance to his Latin-flavored brand of Communism, the problem was youth. And the revelation that most startled Castro's audience of hundreds of thousands in the plaza was that some youths had destroyed posters of the late guerrilla hero Che Guevara.

Shouts from the crowd interrupted Castro when he mentioned it, but their substance could not be made out over the radio here.

Guevara posters are displayed all over the island - some larger than life-size. Castro's revelation was the first official word that Guevara's memory, which the regime holds up as an example for all Cubans, is not universally revered.

Castro said the same youths have destroyed Cuban flags, school materials and telephones, and committed "thefts and delinquent acts."

His main criticism, however, was directed at a revival of prostitution in the heart of Havana. The same youths, "and some not so young," were said to have gathered regularly for months near the Hotel Capri and on other nearby streets and recruited girls 14 to 16 years old for prostitution.

He said the girls were "sold to foreigners in transit in this country," including sailors from capitalist countries, and these visitors illegally sold the youths such items as American cigarettes and battery-powered radios.

Castro said that "some hundreds" of young people were involved in the acts he mentioned. Some, he said, were relatives of families that are leaving Cuba, others were "misguided through the carelessness of their own families," and some were influenced by "imperialist propaganda."

Castro warned that his enemies are trying to "sow fear." He said the recent accidental death of a child in a swimming pool at Guanabo was being used in recent days as the basis for "fabulous rumors about kidnapings of children, about acts of vampirism and I don't know how many other things of that kind."