NATO First Act – Expresses U.S. policy on the current force structure in Europe. Prohibits any action to effect or implement the closure of any military installation in a European member nation of the North Atlantic Treaty Organization (NATO) at which a unit of U.S. Armed Forces is based, or to alter the permanent basing arrangement of such a unit, unless: (1) the closure is requested by the government of the host nation; or (2) the Secretary of Defense makes a certification to the congressional defense committees regarding the necessity of such closure or alteration. Authorizes the Secretary to: (1) conduct or support programs to build the capacity of the national military forces of certain foreign countries to support the theater priorities of the Commander of the United States European Command; and (2) provide assistance to the NATO Special Operations Coordination Center to support NATO special operations forces and activities. Expresses U.S. policy on the extended deterrence commitment to Europe. Prohibits any action to effect or implement the reduction of U.S. nuclear forces in Europe unless: (1) the reduction is requested by the government of the host nation; or (2) the Secretary makes certain certifications regarding the necessity of such reduction. Earmarks specified funds appropriated for FY2011-FY2012 for the Missile Defense Agency for a long-range missile defense system in Europe. Directs the Secretary to deploy a system providing a short-range air and missile defense capability, and the personnel required to operate and maintain the system, to Poland. Allows Department of Defense (DOD) funds to be used to implement reductions in the strategic nuclear forces of the United States pursuant to a treaty or other agreement entered into between the United States and the Russian Federation after the date of enactment of this Act only if the President makes certain certifications to Congress concerning the efficacy of such reductions. Authorizes the Secretary to expand the United States-Russian Federation joint center for the exchange of data from early warning systems to include the exchange of data on missile defense-related activities.