  There is observational evidence that central compact objects (CCOs) in
supernova remnants have moderately strong magnetic fields $B\sim10^{11}$ G.
Meanwhile, available models of partially ionized hydrogen atmospheres of
neutron stars with strong magnetic fields are restricted to $B\gtrsim10^{12}$
G. We extend the equation of state and radiative opacities, presented in
previous papers for $10^{12}\mbox{ G}\lesssim B \lesssim 10^{15}$ G, to weaker
fields. An equation of state and radiative opacities for a partially ionized
hydrogen plasma are obtained at magnetic fields $B$, temperatures $T$, and
densities $\rho$ typical for atmospheres of CCOs and other isolated neutron
stars with moderately strong magnetic fields. The first- and second-order
thermodynamic functions, monochromatic radiative opacities, and Rosseland mean
opacities are calculated and tabulated, taking account of partial ionization,
for $3\times10^{10}\mbox{ G}\lesssim B\lesssim 10^{12}$ G, $10^5$ K $\lesssim
T\lesssim 10^7$ K, and a wide range of densities. Atmosphere models and spectra
are calculated to verify the applicability of the results and to determine the
range of magnetic fields and effective temperatures where the incomplete
ionization of the hydrogen plasma is important.
