The paper deals with optimality conditions of variational type for infinite horizon discrete time optimal control problems. We show that for unconstrained problems standard first order conditions extend from a finite to an infinite horizon provided a certain linear operator has closed range. This is the case if the dynamics of the problem has exponential dichotomy, a frequented concept in dynamical systems theory. In addition, closedness of the range allows us to phrase a simple condition for the "normality" of the optimality conditions.