  The lower critical field of the grains, $H_{c1}$, and the intragrain critical
current density, $J_{c}$, were determined for the superconducting
ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10-\delta}$
[Ru-1222(Gd)] through a systematic study of the hysteresis in magnetoresistance
loops. A reliable method, based on the effects of the magnetization of the
grains on the net local field at the intergranular junctions is provided,
circumventing the problem of the strong masking of the superconducting
diamagnetic signal by the ferromagnetic background. The temperature dependency
of $H_{c1}$ and $J_{c}$ both exhibit a smooth increase on cooling without
saturation down to $T/T_{SC}$ $\cong $ 0.2. The obtained $H_{c1}$ values vary
between 150 and 1500 Oe in the 0.2 $\leq $ $% T/T_{SC}$ $\leq $ 0.4 interval,
for samples annealed in an oxygen flow; oxygenation under high pressure (50
atm) leads to a further increase. These values are much larger than the
previously reported rough assessments (25-50 Oe), using conventional
magnetization measurements. High $J_{c}$ values of $% \sim $ 10$^{7}$
A/cm$^{2}$, comparable to the high-T$_{c}$ cuprates, were obtained. The
$H_{c1}(T)$ and $J_{c}(T)$ dependencies are explained in the context of a
magnetic phase separation scenario.
