  The recently discovered tight correlation between supermassive black hole
mass and central velocity dispersion suggests a possibility to estimate the
SMBH mass from the measured central velocity dispersion. However, for most AGNs
it is difficult to measure the central velocity dispersions of their host
galaxies directly. In this paper we adopt the fundamental plane for ellipticals
to estimate the central velocity dispersion and SMBH mass for a number of AGNs
with morphology parameters of their elliptical host galaxies obtained by the
HST imaging observations. The estimated SMBH masses of 63 BL Lac objects, 10
radio galaxies, 10 radio-loud quasars and 9 radio-quiet quasars are mostly in
the range of $10^{7.5} M_\odot$ to $10^{9} M_\odot$. No significant difference
in black hole mass is found for high-frequency peaked BL Lacs and low-frequency
peaked BL Lacs, as well as for radio galaxies and radio-loud quasars. The
Eddington ratios of radio galaxies are substantially smaller than those of
quasars. This suggests that the different observational features of radio-loud
AGNs may be mainly dominated by accretion rate rather than by the black hole
mass, which is in agreement with some evolutionary scenarios recently proposed
for radio-loud AGNs. Different from some previous claims, we found that the
derived mean SMBH mass for radio-loud quasars is only slightly larger than that
of radio-quiet quasars. Though their SMBH mass distributions are statistically
different, their Eddington ratio distributions are probably from the same
population. In addition, we noted that the relation between black hole mass and
host galaxy luminosity obtained using the fundamental plane provides further
arguments for a nonlinear scaling law between SMBH and galactic bulge mass.
