Résumé : Analyses of position and force control laws in the case of perfectly rigid bodies have been made so far with strong assumptions on the state of the contacts such as supposing that they are permanent. We're interested here in having a look at what happens when no such assumptions is made: we are led therefore to propose a Lyapunov stability analysis of a position and force control law in the mathematical frame-work of nonsmooth Lagrangian dynamical systems, a typical example of hybrid dynamical systems.