  We propose that the radion chiral supermultiplet of five dimensional
compactified supergravity is obtained by reduction of the graviphoton gauge
multiplet to N=1 superfields in the off shell 5D superconformal gravity
formalism of Fujita, Kugo and Ohashi. We present a superfield Lagrangian of
Chern-Simons type (similar to global SUSY), which reproduces all component
couplings of gauge fields and the radion. A hypermultiplet superspace action is
also proposed which correctly accounts for the coupling of matter multiplets
with gauge and radion superfields. 4D supergravity enters by the coupling to
the 4D Weyl multiplet, an even orbifold parity multiplet embedded in the 5D
Weyl multiplet. We apply this formalism to a discussion of Fayet-Iliopolous
terms, and the gauging of orbifold SUGRA to obtain warped solutions.
