  This Letter reports on a first measurement of the inclusive W+jets cross
section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the
LHC, with the ATLAS detector. Cross sections, in both the electron and muon
decay modes of the W boson, are presented as a function of jet multiplicity and
of the transverse momentum of the leading and next-to-leading jets in the
event. Measurements are also presented of the ratio of cross sections sigma(W+
\ge n) / sigma(W+ \ge n-1) for inclusive jet multiplicities n=1-4. The results,
based on an integrated luminosity of 1.3 pb-1, have been corrected for all
known detector effects and are quoted in a limited and well-defined range of
jet and lepton kinematics. The measured cross sections are compared to
particle-level predictions based on perturbative QCD. Next-to-leading order
calculations, studied here for n \le 2, are found in good agreement with the
data. Leading-order multiparton event generators, normalized to the NNLO total
cross section, describe the data well for all measured jet multiplicities.
