BEIRUT — A pro-Iranian Muslim cleric said yesterday that a recent statement by Islamic Jihad was "a breakthrough" in years of efforts to free the 12 Western captives in Lebanon.The senior fundamentalist official, who could not be identified, says one of 12 Western hostages in Lebanon may be the "special envoy" that Lebanese kidnappers promised Tuesday to send to the United Nations in 48 hours. Six Americans, three Britons, two Germans, and an Italian are held by militant Muslim groups in Lebanon. But in Washington, President Bush said he knew of no new grounds for optimism about their imminent release. Islamic Jihad, which holds Americans Terry Anderson and Thomas Sutherland, said it wanted to end the ordeal of the Westerners and its envoy would deliver an important message to UN headquarters in New York for Secretary- General Javier Perez de Cuellar. The Arabic statement was accompanied by a photograph of Mr. Anderson, chief Middle East correspondent for the Associated Press news agency. Kidnapped March 16, 1985, he is the longest-held hostage among the 12. The White House reacted with restraint. "Hopes get raised over and over again," Bush said. Mr. Perez de Cuellar said he hoped the announcement was "the beginning of a solution to this tremendous problem." In Beirut, the fundamentalist official told Reuters the statement was a "breakthrough and some sort of opening in a blocked-up wall." He said the kidnappers may use one of the hostages to carry their message to the United States. The statement was delivered to an international news agency in Beirut shortly after the Tehran Times newspaper in Iran reported that an American and a British hostage in Lebanon were likely to be released by the weekend.