  We present an analysis of the ultraviolet and X-Ray variability of the Broad-
Line-Radio Galaxy 3C390.3 over 15 years. The UV continuum showed large
variations with amplitudes of up to a factor of 10. We find: (1) The variations
of CIV and Ly_alpha are highly correlated with the UV continuum, and are
delayed with respect to the continuum variations by 50-110 days with the red
wing of both CIV and Ly_alpha , leading the blue wing; (2) The CIV/Ly_alpha
ratio is positively correlated with both the continuum flux and UV line
strength, a behavior different from other AGNs studied so far; (3) The blue
sides of the Ly_alpha and CIV profiles are similar to the blue side of the
Balmer lines, while the red sides are different, suggesting a different origin
for the red peak in the Balmer lines. Our results suggest: (1) The broad CIV
and Ly_alpha emitting gas is infalling towards the central object; (2) The
overall behaviour of the CIV/Ly_alpha ratio and the absence of a big blue bump,
strongly indicate the coexistence of optically thick as well as optically thin
BLR clouds; (3) Assuming circular symmetry and predominantly circular motion,
the BLR gas is situated at 83$\pm$25 lightdays from the central source; (4)
Under these assumptions and with the derived circular velocity of $v_{rot}
\simeq$ 2850 km s$^{-1}$, the central mass inside this radius is confined to
$1.3~10^8 M\odot < M_{CM}< 4.0~10^8 M\odot$; (6) Comparing our results with
those obtained from VLBI and observations of the Fe $K\alpha$ line, suggests
the association of the BLR with a disk, inclined at 98$\pm$12 degrees with
respect to the direction of superluminal motion of the radio blobs.
