  We obtain an expression for the active gravitational mass (Tolman) of a
source of the $\gamma$ metric, just after its departure from hydrostatic
equilibrium, on a time scale of the order of (or smaller than) the hydrostatic
time scale. It is shown that for very compact sources, even arbitrarily small
departures from sphericity, produce significant decreasing (increasing) in the
values of active gravitational mass of collapsing (expanding) spheres, with
respect to its value in equilibrium, enhancing thereby the stability of the
system.
