Noble metal clusters were generated and stabilized in poly(amide imide) (PAI) polymers in high dispersion and high concentration of typically 15 wt %. The loaded polymers were prepared as pore-free, mechanically stable membranes, which have been successfully tested for catalytic activity in membrane reactors. Pure Pd- and Ag-loaded as well as bimetallic Pd/Ag, Pd/Cu, Pd/Co, and Pd/Pb PAI films were investigated by means of X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to characterize the structure and morphology of the metal clusters in the protective polymer. The measurements consistently show a homogeneous distribution of metallic nanoclusters of 1-3 nm size with a smaller amount of larger aggregates up to 30 nm in some of the films. The precise cluster size and distribution critically depend on the solvents used (N-methyl-2-pyrrolidone, tetrahydrofuran) as well as on other preparation parameters such as the stirring time of the metal precursor/polymer solution. In the case of Pd/Ag and Pd/Pb bimetallic films no clear evidence for the formation of bimetallic clusters in the membrane, i.e. alloying of both metal components, is found. In Pd/Cu and Pd/Co membranes, chlorine from the CuCl2 and CoCl2 precursors reacts with Pd, which may influence the Pd catalytic behavior. Reduction of the oxidized metal nanoclusters by H-2 at 300 K is quantitatively studied by means of XAFS and gas permeation. Optimum membrane preparation conditions are discussed with respect to the cluster formation mechanism.