Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P(2)O(5)r-WO3-A(2)O (A = Li, Na). Structural approach of the highly modified glasses P2O5-A(2)MoO(4)-A(2)O (M = Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO6 octahedra, MO4 tetrahedra, M2O7 dimers, PO4 tetrahedra, and also P2O7 or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A(2)O increases. ESR experiments were conducted on both X-ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W5+ and Mo5+ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus-oxygen-hole-center and peroxy radicals. The M5+ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted or vitreous materials.