  We report VLA HI Zeeman observations toward the W49A star-forming region and
the SNR W49B. Line of sight magnetic fields (Blos) of 60 to 300 muG at 25"
resolution were detected toward W49A at velocities of ~4 and ~7 km/s. The Blos
values measured toward W49A show a significant increase in field strength with
higher resolution especially for the ~4 km/s HI gas. The HI gas in the velocity
range -5 to 25 km/s toward W49A shows good agreement both kinematically and
spatially with molecular emission intrinsically associated with W49A. Based on
comparisons with molecular data toward W49A, we suggest that the 4 km/s HI gas
is directly associated with the northern part of the HII region ring, while the
7 km/s HI gas seems to originate in a lower density halo surrounding W49A. We
estimate that the W49A North core is significantly subvirial, and that the
total kinetic +magnetic energies amount to less than 1/3 of the total W49A
North gravitational energy. These magnetic field results suggest that W49A
North is unstable to overall gravitational collapse in agreement with evidence
that the halo is collapsing onto the W49A North ring of HII regions.
  The majority of the HI column density toward W49B comes from Sagittarius Arm
clouds along the line of sight at ~40 km/s and ~60 km/s. No significant
magnetic fields were detected toward W49B. Comparison of the spectral
distribution of HI gas toward W49A and W49B suggests that evidence placing W49B
3 kpc closer to the sun (i.e. at 8 kpc) than W49A is quite weak.
