Abstract : One of the main goals of the ATLAS experiment is the search for the Higgs boson, the last missing ingredient of the standard model, and the studies of its properties. The experiment will be based at the future proton-proton collider LHC, whose first collisions are expected in 2007. The work presented in this thesis is dedicated to the search for a Higgs boson with a mass below 200 GeV/c2, in the associated production channel pp->ttH. The identification of jets containing b-hadrons is crucial for Higgs boson and top quark studies. The tagging performances of b-jets are studied in details in the ttH, H->bb channel, in the most realistic conditions at start of data taking (reduced pixel detector, pile-up, detection ine ciencies). At 60 % b-jet efficiency, light and c-jet rejections of 80% and 7% respectively are achieved. Whereas the discovery of the Higgs boson is expected to be relatively easy, the measurement of its parameters, in particular its couplings to fermions, is more involved. The possibility of observing the Higgs boson in the ttH, H->WW(*) channel is investigated. This process is the only one to date leading to a direct measurement of the top quark Yukawa coupling in the mass range 130-200 GeV/c2. For a Higgs boson of mass 160 GeV/c2, a statistical precision of ~7% could be reached after three years of data taking at high luminosity.