We report VLA H i Zeeman observations toward the W49A star-forming region and the SNR W49B .
Line of sight magnetic fields ( B _ { los } ) of 60 to 300 \mu G at 25 \arcsec resolution were detected toward W49A at velocities of \sim 4 km s ^ { -1 } and \sim 7 km s ^ { -1 } .
The B _ { los } values measured toward W49A show a significant increase in field strength with higher resolution especially for the \sim 4 km s ^ { -1 } H i component .
The H i gas in the velocity range -5 to 25 km s ^ { -1 } 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 \sim 4 km s ^ { -1 } H i component is directly associated with the northern part of the H ii region ring , while the \sim 7 km s ^ { -1 } H i component seems to originate in a lower density halo surrounding W49A .
We estimate that the W49A North core is significantly subvirial ( 2 { \cal T } / \mid { \cal W } \mid \sim 0.2 ) , 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 H ii regions .

The majority of the H i column density toward W49B comes from Sagittarius Arm clouds along the line of sight at \sim 40 km s ^ { -1 } and \sim 60 km s ^ { -1 } .
No significant magnetic fields were detected toward W49B .
Comparison of the spectral distribution of H i 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 .
Although we can not place W49B at the same distance as W49A , we find the morphology of a \sim 5 km s ^ { -1 } H i component toward the southern edge of W49B suggestive of an interaction .