Abstract : The LHC produced proton-proton collision data with 7 TeV of center of mass energy corresponding to an integrated luminosity of 40 pb-1 in 2010 and of 5 fb-1 in 2011. The data collected by ATLAS have led to the validation the understanding of the detector, to the evaluation of its performance and to many measurements of physical quantities. In this context the top quark is a privileged field of study for TeV scale physics as well as for performance studies. After a reminder of the phenomenology of the standard model the first part of this thesis is devoted to the description of the detector and in particular of the liquid argon calorimeters for which the influence of the variations of the high voltage values is detailed. The second part is focused on studies about the reconstruction and the identification of electrons conducted on simulated data, but also on 2010 collision data thanks to J/psi->e+e- events with the tag-and-probe method. The last part is devoted to top quark studies. A desctiption of the signal and background simulated data for ttbar events is given, as are the reconstruction and identification procedures of the objects present in the final state. The estimation of the contribution of events with a mis-identified lepton thanks to the matrix-method is then presented before the measurement of the ttbar cross-section in dilepton channels made on 2011 data: the value of 178.8 +/-2.3(stat) +8.9/-8.4(sys) +8.0/-7.4(lumi) pb obtained by combining the three channels is compatible with theoretical predictions.