  A model for $La_{1-x}Sr_xMnO_3$ which incorporates the physics of dynamic
Jahn-Teller and double-exchange effects is presented and solved via a dynamical
mean field approximation. In an intermediate coupling regime the interplay of
these two effects is found to reproduce the behavior of the resistivity and
magnetic transition temperature observed in $La_{1-x} Sr_x MnO_3$.
