28 U.S.C. § 2671 : US Code - Section 2671: Definitions

      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.