Until the publication of this book, in a serviceable translation by Andrew Hurley, we had not had a full picture of the brutality meted out to real and imaginary opponents by the Castro dictatorship. What Mr. Valladares gives us is a picture of the hell that was the Cuba he lived in, and the story of how one man's deep Christian faith enabled him to sustain the most evil treatment and never abandon hope, no matter how fruitless hope appeared.

Mr. Valladares and other prisoners who refused ''political rehabilitation'' were forced to live in the greatest heat and the dampest cold without clothes. They were regularly beaten, shot at and sometimes killed; they were thrown into punishment cells, including the dreaded ''drawer cells,'' specially constructed units that make South Vietnam's infamous tiger cages seem like homey quarters. Eventually, together with several others, Mr. Valladares plotted an escape from their prison on the Isle of Pines. But the boat that was to pick them up never arrived. He and his accomplices were brought back to their cells and given no medical attention, though Mr. Valladares had fractured three bones in his foot during the escape attempt.

The retribution was swift. Mr. Valladares writes: ''Guards returned us to the cells and stripped us again. They didn't close the cell door, and that detail caught my attention. I was sitting on the floor; outside I heard the voices of several approaching soldiers. . . . They were going to settle accounts with us, collect what we owed them for having tried to escape. . . . They were armed with thick twisted electric cables and truncheons. . . . Suddenly, everything was a whirl - my head spun around in terrible vertigo. They beat me as I lay on the floor. One of them pulled at my arm to turn me over and expose my back so he could beat me more easily. And the cables fell more directly on me. The beating felt as if they were branding me with a red-hot branding iron, but then suddenly I experienced the most intense, unbearable, and brutal pain of my life. One of the guards had jumped with all his weight on my broken, throbbing leg.''

That treatment was typical. In the punishment cells, prisoners were kept in total darkness. Guards dumped buckets of urine and feces over the prisoners who warded off rats and roaches as they tried to sleep. Fungus grew on Mr. Valladares because he was not allowed to wash off the filth. Sleep was impossible. Guards constantly awoke the men with long poles to insure they got no rest. Illness and disease were a constant. Even at the end, when the authorities were approving his release, Mr. Valladares was held in solitary confinement in a barren room with fluorescent lights turned on 24 hours a day. By then he was partially paralyzed through malnutrition intensified by the lack of medical attention.

Political prisoners, the author reminds us, were not always treated so brutally in Cuba. When Fidel Castro was imprisoned following his attack on the Moncada barracks on July 26, 1953, he was given good food, large and airy quarters, full mail privileges and even conjugal visits. Mr. Castro himself wrote of ''many pleasant hours'' spent in an airy yard, of good dinners with Italian chocolate for dessert and two baths a day. ''They're going to make me think I'm on vacation,'' he quipped in a letter. By his own account, Mr. Castro had ''plenty of water, electric lights, food, clean clothes, and all for free.''