The results of the atomic and electronic structure calculations, with a focus on the surface relaxation and polarization, are presented for the LaMnO₃ (110) O-terminated polar surface. We compare results of the classical shell model (SM) and ab initio Hartree-Fock calculations for three possible surface models, including (1×2) (110) surface reconstruction, and demonstrate that the latter has the lowest surface energy. The surface energy is saturated only when six to eight near-surface atomic planes are relaxed which is accompanied by considerable macroscopic surface polarization. Properties of stoichiometric surfaces with oxygen vacancies and non-stoichiometric defect-free surfaces are compared, along with ferromagnetic and antiferromagnetic (AFM) Mn spin orderings in slabs.