Abstract : While the value of local political participation is being reasserted as a means to remedy the crisis of political activity, the present thesis deals with the kind of deliberation that can be observed on electronic forums of discussion offered in France by local authorities on the Internet. The specific characteristics of electronic forums – the very technical potentialities of this instrument (asynchronic written exchanges, lack of co-presence of participants) and also its uses (anonymous and unselected permanently recorded contributions) – induce a reconsideration of the ways in which citizens may participate in the managing of the city. The observation of municipal websites in towns in three areas in South-West France (Aquitaine, Languedoc-Roussillon and Midi-Pyrénées), the analysis of their forums as well as interviews of municipal agents have led to a more specific study of the arguments and competences summoned by internauts, of the remodelling of hierarchic structures that hinder public speech, of the way municipal authorities format these discourse exchanges and of the conditions of their being articulated to political decision. Empirical data were examined from the viewpoint of different aspects of deliberative theory and comparative method was also applied to other municipal deliberative and participative devices. In this perspective the present research attempts to determine the specific characteristics of electronic deliberation, and the way they reveal significations and tensions as to the capacity of the present political system to proceed to a democratisation of public decision.