The second-order ordering transition of the AuAgZn2 alloy has been studied by coherent x-ray scattering. Within a few degrees above the critical temperature Tc, equilibrium critical fluctuations are observed together with some pre-transitional local ordering connected to sample defects. The speckles observed correspond to heterodyne interference between local ordering and fluctuations and show a mixed static and dynamical behaviour in a narrow domain of a few tenths of degree above Tc. The dynamical behaviour is shown to correspond to the critical slowing down of the fluctuations in the vicinity of the transition (model " A " of Hohenberg and Halperin 1). A rough comparison can be carried out with the classical diffusion models. Some improvements of the method are discussed.