A model of neoclassical tearing modes (NTMs) allowing for a finite width ofthe transition layer near the island separatrix, where perturbed plasmaparameters vary significantly, is proposed. In contrast to traditionalmodels of NTMs, this model includes the parameter ρi/w properly,where ρi is the ion Larmor radius, and w is the magnetic islandwidth. It is shown that both the polarization current and bootstrap currenteffects on these modes prove to be weakened compared with those predicted bytraditional theories of NTMs. The competition of these effects results in acritical beta for NTM onset which is lower than that usually used forinterpretation of experimental observations and predictions for reactor-gradetokamaks.