Longitudinal beam dynamics is investigated in a traveling-wave field with variable synchronous phase assumed to be a control function. The dynamic controlled process is considered to be a complex of synchronous particle motion and the motions of particles of a beam. In generalization, the model is represented by a system of integro-differential equations. The problem of joint optimization of program motion and the ensemble of perturbed motions is formulated. Numerical simulation of beam dynamics is performed; the example of optimization is considered.