  The Novello-DeLorenci-Luciane (NDL) field theory of gravitation predicts that
gravitational waves (GWs) follow geodesics of a modified (effective) geometry
with a speed lower than the velocity of light. The theory also demonstrates
that GWs exhibit the phenomenon of birefringence, formerly believed to be
exclusive of electromagnetic waves. Here prospective astrophysical tests of
these predictions are proposed. I point out that future measurements of
gravitational waves in coincidence with a non-gravitational process such as
{\it a neutrino burst} (and likely a burst of gamma-rays) may prove useful to
discriminate among all the existing theories of gravity. It is also stressed
that microlensing of gravitational waves emitted by known galactic sources
(i.e., pulsars) in the bulge, lensed by either the Galaxy's central black hole
(Sgr A$^\ast$) or a MACHO object adrift among the Milky Way's stars, may
provide a clean test of the birefringence phenomenon implied by the NDL gravity
theory.
