  The 17O and 207Pb NMR spectra were measured in ceramic samples in the
metallic phase of BaPb_{1-x}Bi_{x}O_3 oxides (0<x< 0.33). The inhomogeneous
magnetic broadening which appears due to a distribution of the Knight shifts
was analyzed in detail. It is shown that Bi atoms, which are randomly
incorporated in BaPbO_3 parent compound give rise to an increased conduction
electron spin density within an area which is delimited by its two first cation
shells. According to NMR data the percolative overlap of these areas occurs in
superconducting compositions and it is accompanied by a sharp growth of the
average Knight shift <Ks>. The decrease of <17Ks> with temperature revealed for
x=0.33 evidences for an opening of the energy gap near E_F near the
metal-semiconductor transition (x=0.35).
