Superspace actions on coadjoint orbits of graded infinite-dimensional groups

The method of coadjoint orbits of infinite-dimensional Lie groups for derivation of geometric D=2 field theory actions is extended to the super-Kač-Moody and super-Virasoro groups in a manifestly (1,0) supersymmetric form. In this way we derive the explicit expressions for the actions of the supersymmetric chiral Wess-Zumino-Novikov-Witten (WZNW) model and of the induced supergravity (the super-gravitational Polyakov action). The latter action is also obtained in a different form by gauging the supersymmetric chiral SL(22,R) WZNW model in the manifest superspace formalism.