A unified model of nuclear reactions taking account of both the compound and preequilibrium nuclear reactions is proposed in terms of a renormalization of the wave functions generated by the optical model potential. The cross sections of the nuclear reactions including preequilibrium processes are formulated, which are especially suited for calculations of cross sections of those nuclear reactions in which the residual nuclei are in discrete levels or isomeric states. The model is used to investigate the reactions [sup 59]Co([ital n],2[ital n])[sup 58]Co and [sup 93]Nb([ital n],2[ital n])[sup 92]Nb. The results are in good agreement with the experimental data.