Electron tunneling in a molecular wire with defects of the type ...AAABAAA..., where electronic states of molecules, host (A) and guest, at different sites are coupled via resonant interaction, is investigated. The model described by a simple Hamiltonian in the tight-binding representation bears at the same time a close resemblance to a double-barrier resonant heterostructure. Resonant tunneling is considered in the presence of an external electric field with the Hubbard electron-electron interaction at the guest site included