The paper is concerned with an optimal control problem governed by a state equa- tion in form of a generalized abstract operator di erential equation involving a maximal monotone operator. The state equation is uniquely solvable, but the associated solution operator is in general not G^ateaux-di erentiable. In order to derive optimality conditions, we therefore regularize the state equation and its solution operator, respectively, by means of a (smoothed) Yosida approximation. We show convergence of global minimizers for regularization parameter tending to zero and derive necessary and su cient optimality conditions for the regularized problems. The paper ends with an application of the abstract theory to optimal control of homogenized quasi-static elastoplasticity.