  We present a new estimate of the projected X-ray mass of Abell 1689 observed
with Chandra, in an attempt to clarify the issue of whether or not there exists
a discrepancy between X-ray and gravitational lensing mass estimates claimed in
previous investigations based on {\it Einstein}, {\it ROSAT} and {\it ASCA}
observations. A particular attention is paid to examining if there is an offset
between X-ray centroid and central dominant cD galaxy, which may be an
indicator of the presence of local dynamical activities of intracluster gas in
the central core and therefore, explain the discrepancy between X-ray and
lensing mass estimates, if any. The unprecedentedly high spatial resolution
achieved by Chandra allows us to precisely localize the X-ray centroid of Abell
1689, which appears to coincide perfectly with the central cD galaxy. This
fact, along with the symmetry and regularity of the X-ray surface brightness
and temperature distributions, suggests that Abell 1689 is a fully-relaxed
cluster. We thus employ hydrostatic equilibrium hypothesis to determine the
projected mass profile of Abell 1689, and compare it with the results obtained
by different lensing techniques available in the literature. Our analysis
confirms the existance of the discrepancy of a factor of $\sim2$ between X-ray
and lensing mass estimates in the central region of $r\approx0.2$ Mpc, although
the two methods yield essentially consistent result on large radii. If the
perfect coincidence between the X-ray center and the cD galaxy of Abell 1689
detected by Chandra observation is not a projection effect, the central mass
discrepancy between X-ray and lensing measurements may pose a challenge to our
conventional understanding of dynamical evolution of the intracluster gas in
the central regions of clusters.
