We have evaluated the optical conductivity over a broad spectral range of single phase K3C60 and Rb3C60 compounds both below and above the superconducting transition temperature. In the superconducting state we found gap values consistent with the BCS weak coupling limit. Moreover, we calculated the electrodynamic response with the standard Eliashberg electron-phonon theory of superconductivity, which strongly supports a pairing mechanism mediated by high frequency intramolecular phonon modes.