  We study numerically the collapse of non-rotating, self-gravitating,
magnetized, singular isothermal toroids characterized by sound speed, $a$, and
level of magnetic to thermal support, $H_0$. In qualitative agreement with
previous treatments by Galli & Shu and other workers, we find that the
infalling material is deflected by the field lines towards the equatorial
plane, creating a high-density, flattened structure -- a pseudodisk. The
pseudodisk contracts dynamically in the radial direction, dragging the field
lines threading it into a highly pinched configuration that resembles a split
monopole. The oppositely directed field lines across the midplane and the large
implied stresses may play a role in how magnetic flux is lost in the actual
situation in the presence of finite resistivity or ambipolar diffusion. The
infall rate into the central regions is given to 5% uncertainty by the formula,
$\dot M = (1+H_0)a^3/G$, where $G$ is the universal gravitational constant,
anticipated by semi-analytical studies of the self-similar gravitational
collapses of the singular isothermal sphere and isopedically magnetized disks.
The introduction of finite initial rotation results in a complex interplay
between pseudodisk and true (Keplerian) disk formation that is examined in a
companion paper.
