  The quartet condensation model (QCM) is extended for the treatment of
isovector and isoscalar pairing in odd-odd N=Z nuclei. In the extended QCM
approach the lowest states of isospin T=1 and T=0 in odd-odd nuclei are
described variationally by trial functions composed by a proton-neutron pair
appended to a condensate of 4-body operators. The latter are taken as a linear
superposition of an isovector quartet, built by two isovector pairs coupled to
the total isospin T=0, and two collective isoscalar pairs. In all pairs the
nucleons are distributed in time-reversed single-particle states of axial
symmetry. The accuracy of the trial functions is tested for realistic pairing
Hamiltonians and odd-odd N=Z nuclei with the valence nucleons moving above the
cores $^{16}$O, $^{40}$Ca and $^{100}$Sn. It is shown that the extended QCM
approach is able to predict with high accuracy the energies of the lowest T=0
and T=1 states. The present calculations indicate that in these states the
isovector and the isoscalar pairing correlations coexist together, with the
former playing a dominant role.
