LEBANESE kidnappers said yesterday they would free American hostage Joseph Cicippio within 48 hours in a United Nations-brokered swap for Arab prisoners held by Israel.The pro-Iranian Revolutionary Justice Organization (RJO) said the decision followed mediation involving the UN, Iran, Syria, Israel, Lebanon, and groups holding five Western hostages in Lebanon. "Positive results and a comprehensive solution which will achieve all parties' interests and demands to close this file for good have been reached," said the RJO statement delivered to an international news agency in Beirut. Israel's Lebanese militia allies released 25 Arab prisoners in Lebanon. The Israeli Defense Ministry said the move was a personal gesture to UN Secretary-General Javier Perez de Cuellar. "The UN secretary-general requested Israel make a personal gesture toward him that would aid him in the overall processes of the mission he has initiated," the ministry said. Mr. Cicippio, deputy comptroller at the American University of Beirut, was kidnapped on Sept. 12, 1986. His expected freedom follows the return to the Middle East of UN troubleshooter Giandomenico Picco on a mission to end the hostage saga by Christmas. Cicippio would be the seventh hostage to be freed since August, and his release would leave four Western hostages in Lebanon - Americans Alann Steen and Terry Anderson, and Germans Heinrich Struebig and Thomas Kemptner.