First measurements of the W ¿ l¿ and Z/¿ * ¿ ll (l = e, µ) production cross sections in proton-proton collisions at s=7TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W ¿ l¿ and 179 Z/¿ * ¿ ll candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb. The measured total W and Z/¿ *-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are Wtot. BR(W ¿ l¿) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and totZ BR(Z/¿ * ¿ ll) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09(lumi) nb (within the invariant mass window 66 < m ll < 116GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W + and W - production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.