BACK room politicking behind the closed doors of Cuba's Communist Party Congress may spark a movement within the Cuban Army to unseat a foundering Fidel Castro. If this happens, Castro would ironically face the same fate as Fulgencio Batista, the dictator he overthrew.An unsuccessful 1956 Army coup, led by Col. Ramon Barquin, shattered the unity of Batista's military and facilitated Castro's rise to power; by the end of 1958, all US military aid to Cuba was cut off and Batista had fled the island. Similarly, the 1989 execution of popular Gen. Arnaldo Ochoa - for allegedly plotting against Castro - heightened tensions within the Cuban military that are now being exacerbated by the Soviet military pullout. Historical parallels between the cases of Colonel Barquin and Ge neral Ochoa suggest that the Cuban Army will establish itself as a power broker as the Castro succession plays out. Barqus effort to topple Batista in 1956 was followed by massive purges of the Cuban Army's professional corps; Batista replaced the professionals with politically reliable lackeys who were unable to crush Castro's guerrilla movement. Ochoe's execution was followed by a massive purge of professional officers in Cuba's Western Army, which defends metropolitan Havana. To fill the security vacuum, Castro has staffed the Western Army with a cadre of officers that are personally loyal to him. With 1.6 million of its 10.4 million citizens engaged in defense, Cuba remains one of the world's most militarized societies. Army officers dominate the Central Committee of Cuba's Communist Party to a greater extent than their counterparts in China or in the former Soviet Union. Because of its leadership role in the government, the Army is the only national institution currently capable of carrying out a transition toward a more open political system. Facing a deteriorating economic situation, Castro has launched "Option Zero," a harsh austerity program that forces extreme sacrifices on the Cuban people in the name of the socialist revolution. Basic food items and even tobacco are now tightly rationed; desperate efforts are being made to circumvent the US trade embargo and to generate hard currency for the flagging Cuban economy. But while Cuban civilians go hungry on "Option Zero" diets, Army collective farms, supermarkets, clinics, and industries ar e increasing their levels of productivity for the exclusive benefit of the military class. In a recent interview in the Communist Party newspaper Granma, Gen. Ramon Pardo, deputy commander of Cuba's Western Army, said the Army is advancing the revolution by achieving self-sufficiency in food and energy resources. But increasingly, Cuba's military functions as a state within a state. As in Batista's time, Castro's efforts to appease his Army camouflage growing concerns within the military over the future of their institution and their personal well-being in a post-Castro Cuba. The Army officer who could best maintain the balance of power in Cuba is Gen. Abelardo Colome Ibarra. As a teen-ager, "Furry" Colome was attracted to the urban underground movement run by Castro's rival, Frank Pais. Colome acted as liaison between the urban movement and Castro's guerrilla front. He performed outstanding service to the revolution, commanding a column under Fidel's brother Raul. Colome was identified by the Central Intelligence Agency in 1974 as director of Cuba's KGB-trained counterintelligence service. He was named commander of the 40,000 Cuban troops in Angola in 1977, preceding his friend Ochoa. Although Colome is the Interior Minister, the First Deputy Minister of Defense, and a member of the Council of State, the Central Committee, and the Politburo of the Communist Party, he shuns the perquisites of power and is known to prefer negotiation over polemics. Colome is the mos t powerful man in Cuba after Fidel and Raul Castro. Another key figure is Army Chief of Staff Gen. Ulises Rosales del Toro. A "soldier's soldier," and a member of the National Assembly, General Rosales is the most respected commander within the Cuban military infrastructure and could mobilize supporters in the Army and the National Assembly in support of a new political movement. With the communist bureaucracy and ordinary citizens demoralized by the withdrawal of Soviet aid, Cuban society is drifting away from Fidel's control. In spite of its Soviet training, Cuba's Army remains a classic Latin military organization that could have taught its hard-line friends in Moscow something about pulling off a coup. If a bloody revolution within the revolution is to be avoided, the Cuban Army will be the instrument of action against Castro in his final days.