  The complete structure of curvature squared terms is analyzed in the context
of chirally extended supergravity, with special emphasis on the gravitationally
induced Fayet-Iliopoulos D--term. Coupling of (chiral) matter is discussed in
relation with a possible extension to U(1) supergravity of the equivalence
mechanism between $\cR+\al\cR^2$ and General Relativity coupled to a scalar.
