Final answer:
The National Security Agency, known as the NSA, provides IT and communications support to the White House, Secretary of Defense, and military sectors for U.S. defense.
Step-by-step explanation:
The organization that provides IT and communications support to the White House, Secretary of Defense, and all military sectors that contribute to the defense of the United States of America is the National Security Agency (NSA). The NSA operates under the authority of the Department of Defense and is responsible for the collection and analysis of foreign communications and foreign signals intelligence, which contributes to the defense of the nation. It also plays a pivotal role in protecting U.S. government communications and information systems from security threats, ensuring the integrity and availability of critical military and intelligence networks.