A quantum Monte Carlo method for obtaining multideterminant Jastrow-Slater wave functions for which the energy is stationary with respect to variations of CI coefficients is presented. It is a generalization of a recently developed approach to the optimization of single particle functions [C. Filippi and S. Fahy, J. Chem. Phys. 112, 3523 (2000)]. Using ground state calculations of the atoms Be, C, and Ne and the dimer Si-2 as illustrative examples, the method is shown to converge rapidly and to significantly lower the energy in most cases.