There is no single “most powerful” government agency; power depends on whether you measure it by financial control, legal authority, or intelligence gathering. [1]

Different agencies hold supreme power in their respective domains: [1]

• Financial Control: The Office of Management and Budget (OMB) is often cited as the most powerful federal agency. It directs all federal agencies, implements the President’s agenda, and controls the budgets of the entire government. [1]
• Regulatory Power: The Office of Information and Regulatory Affairs (OIRA), a tiny White House sub-agency, acts as a gatekeeper for almost all federal regulations, holding the power to approve, block, or water down rules for major industries. [1, 2]
• Domestic Law Enforcement: The Federal Bureau of Investigation (FBI) wields the broadest domestic jurisdiction, uniquely combining intelligence-gathering capabilities with the power to arrest and investigate federal crimes within the United States. [1, 2]
• Global Intelligence & Covert Action: The Central Intelligence Agency (CIA) is the premier foreign intelligence service, wielding enormous geopolitical influence through covert action and the collection of vital information to safeguard national security. [1, 2]
• Technical Surveillance: The National Security Agency (NSA) commands unparalleled power in global cyber-capabilities and signals intelligence. [1]

Context on financial and regulatory power is detailed further in the OMB and OIRA mandates.