  Superconducting phase transitions in strongly type-II superconductors in the
Pauli paramagnetic limit are considered within the framework of the
Gorkov-Ginzburg-Landau approach in the lowest Landau level approximation for
both s and d-wave electron pairing. Simple analytical expressions for the
quadratic and quartic coefficients in the order parameter expansion of the
superconducting free energy are derived without relying on gradient or
wavenumber expansions. The existence of a changeover from continuos to
discontinuos superconducting phase transitions predicted to occur in the clean
limit is shown to depend only on the dimensionality of the underlying
electronic band structure. Such a changeover can take place in the quasi 2D
regime below a critical value of a 3D-2D crossover parameter.
