  We show that duality transformations of linearized gravity in four
dimensions, i.e., rotations of the linearized Riemann tensor and its dual into
each other, can be extended to the dynamical fields of the theory so as to be
symmetries of the action and not just symmetries of the equations of motion.
Our approach relies on the introduction of two "superpotentials", one for the
spatial components of the spin-2 field and the other for their canonically
conjugate momenta. These superpotentials are two-index, symmetric tensors. They
can be taken to be the basic dynamical fields and appear locally in the action.
They are simply rotated into each other under duality. In terms of the
superpotentials, the canonical generator of duality rotations is found to have
a Chern-Simons like structure, as in the Maxwell case.
