  The dependence of the moment of inertia $\cal J$ on the pairing and axial
quadrupole deformation $\beta$ in $^{24}$Mg and $^{20}$Ne was investigated. The
study is based on quadrupole-constrained calculations with three cranking
approaches for $\cal J$ (Inglis-Belyaev, Thouless-Valatin, adiabatic
time-dependent Hartree-Fock) and a representative set of Skyrme forces (SVbas,
SkM*, SLy6). At variance with macroscopic collective models, the calculations
predict the specific regime $d{\cal J}/d\beta<0$ at $\beta \ge 0.5$ ($^{24}$Mg)
and $\beta \ge 0.6$ ($^{20}$Ne), where the pairing breaks down. This regime is
explained by two effects: full break up of the pairing and specific evolution
of a {\it single} dominant particle-hole (1ph) configuration with $\beta$. The
analysis of experimental data for the ground-state rotational bands in
$^{24}$Mg and $^{20}$Ne shows that such regime is possible at low spins.
