Italy says it will contribute 2,700 troops to the military campaign against terrorism.
Defence minister Antonio Martino has asked Parliament to give bipartisan support to the government's request to join the US-led coalition when it votes later today.
Italy's contingent will include naval, air and ground components.
Among resources Italy placed at Washington's disposal were the aircraft carrier Garibaldi, with Harrier jump jets and attack helicopters, transport and fuel supply planes, and around 1,000 soldiers for mainly escort and humanitarian missions.
Martino said the majority of Italy's military contribution would be to logistical and defensive operations, but added that a limited portion of the contingent might be involved in combat operations.
Premier Silvio Berlusconi's centre-right coalition has a comfortable majority in both houses of parliament.
Centre-left opposition leader Francesco Rutelli said the legislature "should be united on such a fundamental issue", although he acknowledged the opposition was divided.