  One of a family previously proposed ``central engines'' for cosmic gamma-ray
burst sources (Klu\'zniak & Ruderman 1998) is considered in some detail. A
steadily accreting $10^6$ Gauss magnetic white dwarf should ultimately collapse
to a strongly differentially rotating, millisecond-rotation-period neutron star
for a wide range of steady accretion rates and initial masses if the accreting
white dwarf has an evolved O-Ne-Mg composition. A similar neutron star could
also result from an initial C-O white dwarf but only for more constrained
accretion rates. Because the collapsing white dwarf begins as a $\gamma=4/3$
polytrope, the final neutron star's spin-rate increases strongly with
cylindrical radius. A stable wind-up of the neutron star's poloidal magnetic
field then produces buoyant magnetic toroids which grow, break loose, rise, and
partly penetrate the neutron star surface to form a transient, $B\approx
10^{17}$ G millisecond spin-period pulsar with a powerful pulsar wind (Usov
1992). This pulsar wind emission is then rapidly suppressed by the surface
shear motion from the strong stellar differential rotation. This wind-up and
transient pulsar formation can occur at other times on different cylinders
and/or repeat on the same one, with (re-)wind up and surface penetration time
scales hugely longer han the neutron star's millisecond spin period. In this
way, differential rotation both opens and closes the doors which allow neutron
star spin-energy to be emitted in powerful bursts of pulsar wind. Predictions
of this model compare favorably to needed central engine properties of
gamma-ray burst sources (total energy, duration, sub-burst fluctuations and
time scales, variability among burst events, and baryon loading).
