A microscopic theory based upon the model of molecular defect volume fluctuations is developed to provide an interpretation of the ultraslow mode and excess static light scattering intensity observed in supercooled glass-forming liquids. By including the defect volume as a variable in the set of slow variables comprising of the number density and momentum density, it is shown that in an one component viscoelastic fluid, a diffusive mode associated with the fluctuations of defect volume is present, in addition to the usual q independent structural relaxation mode associated with density fluctuations. Fluctuations of defect volume arise from the configurational rearrangement of molecules. A two fluid model previously proposed for interpreting the anomalous quasielastic light scattering results in an one component fluid follows naturally from the present model.