The limited basis set Hartree—Fock problem is solved in the presence of a perturbation term in the Hamiltonian to obtain the first-order perturbed wavefunction. The formulation is applied to the calculation of electric polarizability, magnetic susceptibility, and magnetic shielding. The effect of the limited basis set on the gauge invariance of the magnetic quantities is discussed. The magnetic susceptibility and shielding, the rotational magnetic moment, and the spin rotational constants are calculated for lithium hydride using two different wavefunctions. The agreement with experiment is reasonably good for the spin rotational constants and rotational magnetic moment. It is felt that further refinement of the calculation would not change the results by more than a few percent.