For the Nambu-Jona-Lasinio model in the regime of dynamical symmetry breaking we formulate principles for selecting 4-fermion models as a low-energy approximation of QCD. On their basis, by means of an effective potential, we consider the possibility of their intrinsic stabilization at a finite cutoff momentum Λ. In the framework of the approach, we investigate the influence of the gluon condensate on the parameters of the model and the effective lagrangian in the low-energy region.