  We generalize the analytical expressions for the two-loop leading-log neutral
Higgs boson masses and mixing angles to the case of general left- and
right-handed soft supersymmetry breaking stop and sbottom masses and
left--right mixing mass parameters ($m_Q, m_U, m_D, A_t, A_b$). This
generalization is essential for the computation of Higgs masses and couplings
in the presence of light stops. At high scales we use the minimal
supersymmetric standard model effective potential, while at low scales we
consider the two-Higgs doublet model (renormalization group improved) effective
potential, with general matching conditions at the thresholds where the squarks
decouple. We define physical (pole) masses for the top-quark, by including QCD
self-energies, and for the neutral Higgs bosons, by including the leading
one-loop electroweak self-energies where the top/stop and bottom/sbottom
sectors propagate. For $m_Q=m_U=m_D$ and moderate left--right mixing mass
parameters, for which the mass expansion in terms of renormalizable Higgs
quartic couplings is reliable, we find excellent agreement with previously
obtained results.
