[en] This thesis presents inclusive e^±p double and single differential cross section measurements for neutral current deep inelastic scattering of longitudinally polarized leptons on protons as a function of the negative four-momentum transfer squared Q² and the Bjorken variable x. The data were collected in the years 2003-2007 in the H1 experiment at HERA with positively and negatively longitudinally polarized lepton beams of 27 GeV and a proton beam of 920 GeV corresponding to the centre-of-mass energy of √(s)=319 GeV. The integrated luminosity is about 330 pb^-1. An overview of the phenomenology of the deep inelastic scattering is given and the experimental apparatus is described. The NC cross section measurement procedure is presented and discussed in details. The measured cross sections are used to investigate electroweak effects at high Q². The proton structure function xF₃, sensitive to the valence quarks in the proton, is measured. The polarization effects sensitive to the chiral structure of neutral currents are investigated. The Standard Model predictions are found to be in a good agreement with the measurement.