  Pure gauge representation for general vacuum background fields (Cartan forms)
in the generalized $AdS$ superspace identified with $OSp(L,M)$ is found. This
allows us to formulate dynamics of free massless fields in the generalized
$AdS$ space-time and to find their (generalized) conformal and higher spin
field transformation laws. Generic solution of the field equations is also
constructed explicitly. The results are obtained with the aid of the star
product realization of ortosymplectic superalgebras.
