  We propose the model for magnetic properties of the magnetic superconductor
RuSr$_{2}$GdCu$_{2}$O$_{8}$, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line $T_{d}(h)$, on
which the Josephson coupled superconducting planes are decoupled, i.e. $%
j_{c}(T_{d})=0$, is calculated as a function of the exchange energy $h$. As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field $H_{c1}$, Josephson plasma frequency, etc. is realized
near (or by crossing) the $T_{d}(h)$ line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSr$_{2}$GdCu$_{2}$O$_{8}$ with possible weak ferromagnetic order in the RuO
planes.
