28 U.S.C. § 2671

As used in this chapter and sections 1346(b) and 2401(b) of this title, the term “Federal agency” includes the executive departments, the judicial and legislative branches, the military departments, independent establishments of the United States, and corporations primarily acting as instrumentalities or agencies of the United States, but does not include any contractor with the United States. “Employee of the government” includes (1) officers or employees of any federal agency, members of the military or naval forces of the United States, members of the National Guard while engaged in training or duty under section 115, 316, 502, 503, 504, or 505 of title 32, and persons acting on behalf of a federal agency in an official capacity, temporarily or permanently in the service of the United States, whether with or without compensation, and (2) any officer or employee of a Federal public defender organization, except when such officer or employee performs professional services in the course of providing representation under section 3006A of title 18 . “Acting within the scope of his office or employment”, in the case of a member of the military or naval forces of the United States or a member of the National Guard as defined in section 101(3) of title 32 , means acting in line of duty.