Fidel Castro's revolution, troubled by continuing economic difficulties, may be facing an increasingly restive population. In recent months, there have been fresh reports of unhappiness among Cuba's blacks, as well as suggestions of incipient student unrest on university campuses.
Now comes official word of a government crackdown on ''counterrevolutionaries'' accused of acts of sabotage on factories and crops - and hints that some of these Cubans may have been trying to organize a Polish-style Solidarity trade union in Cuba. At least 33 Cubans have recently been tried and given ''severe'' prison sentences for antigovern- ment activity.
But Roberto Veiga, who heads the government-run Cuban Trade Union Federation, denies that any of those sentenced were trying to form a Solidarity-type union.
Cuban exile sources, as well as human rights organizations, are sticking by their allegations that five Cubans recently were sentenced to death for attempts to form such a union.
Moreover, rumors have circulated in Cuba for weeks that hundreds of sugar cane workers were arrested earlier this year on charges of trying to set up independent union activities in Cuba.
Whatever is actually taking place, there can be no mistaking the evidence that Cuba's leadership faces more opposition today than would have seemed possible a few years ago.
Perhaps this should not seem surprising. After all, Dr. Castro has been in power for nearly 25 years, having toppled the Batista dictatorship on Jan. 1, 1959. Despite the heady enthusiasm with which he and his government were received in the early years and the support they continue to enjoy, opposition was bound to grow with the years.
Some of the early support was sparked by the Castro government's achievements in housing, education, and health care. But those advances took place 15 to 20 years ago. Some Cubans now are asking, in effect, what do we get for an encore?
Then, too, the promise of an improving economic climate for the Caribbean island simply has not materialized. Few Cubans can overlook this situation with its shortages of many basic foodstuffs and consumer items. Rationing has been a part of the Cuban system for most of the Castro years. Dr. Castro frequently admits that this is unlikely to change in the near future. He also regularly exhorts Cubans to sacrifice for the revolution.
Moreover, for many Cubans, the heavy hand of Castro's rule runs counter to their natural instincts for an open society.
No one suggests that Castro's hold on power is seriously threatened. But 25 years after coming to power, he is facing growing internal discontent. And Cuba is not aloof from trends such as student protest and even trade union formation so evident elsewhere.