Last Boat From Mariel : THE PEREZ FAMILY <i> by Christine Bell (W. W. Norton: $19.95; 256 pp.) </i>

The whim of Fidel Castro, or Cuban prison authorities, achieves the release of Juan Raul Perez at the start of this ambitious work of fiction by Christine Bell, author of “Saint.”

After 20 years’ incarceration, Perez finds himself a free man embarked for the United States on one of the last boats to sail during the Mariel boat lift of 1981. Bald, toothless, underweight, he is not quite the man his wife left behind. His biggest fear is that his wife (“his reason for existence”) may be dead or remarried, or unable to recognize “the toothless old man he had become.”

His wife, Carmela, has waited for him. When the Mariel boat lift began, she made room in her closet and dressers to accommodate Juan Raul’s clothes. But she has lost heart. Her brother, Angel, has hired a variety of boats--yachts, fishing boats--with no luck. He waited for two days when he rode on one of the boats himself, getting sunburned and bitten by mosquitoes. But the load of passengers that the Cuban authorities released was a family of eight strangers.

Immigration services are well acquainted with Angel, who asks with every boat-load whether a single man named Juan Perez has arrived. He is told there are a number of Juan Perezes, but none are single.

That is because American immigration officials have mistaken Juan Raul and another passenger, Dorita Evita Perez, for husband and wife--they share the same last name.

Dorita Evita (who calls herself Dottie) provides a lust for life to fill what Juan Raul lacks. She got her release when she told Cuban authorities she wanted to leave for “John Wayne, Elvis Presley, rock and roll, blue jeans, nail polish . . . everything you say I cannot have.” The authorities labeled her unfit and put her on a boat out of Mariel harbor.

Dottie hears that it would expedite their gaining a sponsor if in fact they were a family (“I ask a lot of questions,” she tells Juan), and Juan Raul is persuaded not to risk being on his own. He allows her to adopt a silent old man dressed in fatigues and carrying a knapsack--whom they’ll call Papa--and a young man to pass as their son, Felipe Perez.

Humor seasons the pathos of these characters. Juan Raul chases the old man (who tends to roam) and has to wash him, sometimes with his fatigues still on. Dottie finds her John Wayne in one of the security guards, Esteban Santesteban, and makes her interest abundantly clear, causing a near-slapstick turn of events.

Another refugee, Luz Paz, is unaware that theirs is a marriage of convenience and views this guard as a home wrecker. After sending her prayers to San Lazaro (patron saint of the poor), Luz Paz gives a gold coin to Felipe Perez to buy some dentures for the toothless old man to improve his looks. Felipe collides with an Impala pulling a Plexiglas-enclosed trailer carrying a another statue of San Lazaro and is knocked unconscious.

Regardless of events taking place around him, Juan Perez writes notes to his wife, with whom he has not communicated in more than a year. “Oh my Love, I am alive . . . I long for you as I have longed for you for 20 years.” But he never sends the letters.

When Juan Raul (wearing “a lime-green parrot shirt and bell-bottoms”) musters the courage to approach her house midway through the book, he inadvertently sets off a burglar alarm that Angel has installed. (Angel bought her a pistol and had an instructor at a shooting range teach her to shoot--in protection against the Marielitos.) Carmela tells the police officers who respond that there was something familiar about the alleged burglar: “I had this uncanny feeling that I had seen him before . . . He reminded me of the old beggars in Havana Square when I was a little girl.”

This scene reflects the difficulty that assimilated Cubans had in accepting the new immigrants of the Mariel boat lift. Castro, having emptied his prisons, caused such unfortunates as Juan Perez to be prejudged unjustly as Fidel’s bad joke.

The novel concludes on a semi-sweet note, an acting-out of a worn Cuban joke about the number of Cubans named Perez. Flavia (Angel’s fiancee), a singer performing at an outdoor concert, arranges to have Carmela and Juan Raul Perez both attend her concert. When she calls for Mr. and Mrs. Juan Perez “to be reunited on the dance floor after 20 years of separation, two people she had never seen before ran into each other’s arms. The crowd went wild.”

The cast of Cubans behaves at times almost like caricatures of themselves, with very funny exaggerated passions and typically Latin outbursts. Bell’s novel successfully combines historical verity and a subtle seriousness with the humor and laughs that are her trademark.