  We report on a 25 ks observation of the 8.7 s anomalous X-ray pulsar
4U~0142+61 with the High Energy Transmission Grating Spectrometer (HETGS) on
the Chandra X-ray Observatory. The continuum spectrum is consistent with
previous measurements and is well fit by an absorbed power-law + blackbody with
photon index Gamma=3.3+/-0.4 and kT=0.418+/-0.013 keV. No evidence was found
for emission or absorption lines, with an upper limit of ~50 eV on the
equivalent width of broad features in the 2.5-13 A (0.95-5.0 keV) range and an
upper limit of ~10 eV on the equivalent width of narrow features in the
4.1-17.7 A (0.7-3.0 keV) range. If the source is a magnetar, then the absence
of a proton cyclotron line strongly constrains magnetar atmosphere models and
hence the magnetic field strength of the neutron star. We find no strong
features that are indicative of cyclotron absorption for magnetic field
strengths of (1.9-9.8)x10^{14} G. This is still consistent with the dipole
field strength of B=1.3x10^{14} G (at the polar cap) estimated from the
pulsar's spindown.
