"We can still stop the country from completely disintegrating and stop Daesh from advancing," Gentiloni said as he announced the December 13th date to the Italian senate, using another name for Isis.
"We can do it, with intense diplomacy, an agreement between the various sides, and a strong commitment to political stability by the future government," he said.
"We don't have much time left," he added, saying it was "out of the question" to let Isis spread any further in the war-torn country.
Libya was thrown into chaos after a 2011 revolt backed by an international military intervention overthrew slain dictator Moamer Kadhafi.
Isis now controls Kadhafi's hometown of Sirte in the east, and experts say the town has become a new focal point for the jihadist group as it comes under increasing pressure in its traditional Iraqi and Syrian power bases.
Meanwhile, two governments vie for power and armed groups battle over the country's energy resources.
Gentiloni's announcement came after he met in Brussels with several of his Nato counterparts on Tuesday and Wednesday.