  We report the precise optical and X-ray localization of the 3.2 ms
accretion-powered X-ray pulsar XTE J1814-338 with data from the Chandra X-Ray
Observatory as well as optical observations conducted during the 2003 June
discovery outburst. Optical imaging of the field during the outburst of this
soft X-ray transient reveals an R = 18 star at the X-ray position. This star is
absent (R > 20) from an archival 1989 image of the field and brightened during
the 2003 outburst, and we therefore identify it as the optical counterpart of
XTE J1814-338. The best source position derived from optical astrometry is R.A.
= 18h13m39.s04, Dec.= -33d46m22.3s (J2000). The featureless X-ray spectrum of
the pulsar in outburst is best fit by an absorbed power-law (with photon index
= 1.41 +- 0.06) plus blackbody (with kT = 0.95 +- 0.13 keV) model, where the
blackbody component contributes approximately 10% of the source flux. The
optical broad-band spectrum shows evidence for an excess of infrared emission
with respect to an X-ray heated accretion disk model, suggesting a significant
contribution from the secondary or from a synchrotron-emitting region. A
follow-up observation performed when XTE J1814-338 was in quiescence reveals no
counterpart to a limiting magnitude of R = 23.3. This suggests that the
secondary is an M3 V or later-type star, and therefore very unlikely to be
responsible for the soft excess, making synchroton emission a more reasonable
candidate.
