  We report the first measurements of inclusive W and Z boson cross sections
times the corresponding leptonic branching ratios for p pbar collisions at
sqrt{s} = 1.96 TeV based on the decays of the W and Z bosons into electrons and
muons. The data were recorded with the CDF II detector at the Fermilab Tevatron
and correspond to an integrated luminosity of 72.0 +/- 4.3 pb-1. We test e-mu
lepton universality in W decays by measuring the ratio of the W->mu nu to W->e
nu cross sections and determine a value of 0.991 +/- 0.004(stat.) +/-
0.011(syst.) for the ratio of W-l-nu couplings (g_mu/g_e). Since there is no
sign of non-universality, we combine our cross section measurements in the
different lepton decay modes and obtain sigma*BR(W->lnu) = 2.749 +/-
0.010(stat.) +/- 0.053(syst.) +/- 0.165(lum.) nb and
sigma*BR(gamma*/Z->ll)=254.9 +/- 3.3(stat.) +/- 4.6(syst.) +/- 15.2(lum.) pb
for dilepton pairs in the mass range between 66 GeV/c^2 and 116 GeV/c^2. We
compute the ratio R of the W->lnu to Z->ll cross sections taking all
correlations among channels into account and obtain R=10.84 +/- 0.15(stat.) +/-
0.14(syst.) including a correction for the virtual photon exchange component in
our measured gamma*/Z->ll cross section. Based on the measured value of R, we
extract values for the W leptonic branching ratio, BR(W->lnu) =0.1082 +/-
0.0022; the total width of the W boson, Gamma(W) =2092 +/- 42 MeV; and the
ratio of W and Z boson total widths, Gamma(W)/Gamma(Z) = 0.838 +/- 0.017. In
addition, we use our extracted value of Gamma(W) whose value depends on various
electroweak parameters and certain CKM matrix elements to constrain the V_CS
CKM matrix element, |V_CS| = 0.976 +/- 0.030.
