Abstract : In this thesis we study the potential of the ATLAS detector at the CERN LHC for discovering supersymmetry (SUSY) in the pp->w1+z2->3l+X channel. Results are given for both low and high luminosity of the LHC. Firstly we establish that SUSY can yield a 5 sigma excess with respect to the Standard Model expectations in the inclusive trilepton topology in a large domain of the SUSY parameter space. We show that SUSY processus other than pp->w1+z2 (SUSY background) may contribute substantially to this excess. Then we refine the event selection in order to increase the purity of the pp->w1+z2->3l+X signal. This enables to study specific properties of this process. In particular we reconstruct the mass difference m(z2)-m(z1). We propose a new method to reconstruct the whole gaugino sector (this method supposes the gaugino masses unification) based on the m(z2)-m(z1) measurement. A chapter deals with the study of the space uniformity of the response of the Hamamatsu R5900 phtomultipliers used for the read-out of the ATLAS hadron calorimeter (Tilecal).