[en] An attempt has been made to calculate the bandwidths of isolated sum resonances of the third and fourth order. From Hamiton's equations and invariants of motion expressions for the effective potential are derived which are examined by the methods of elementary cathastrophe theory. The final result is expressed by the formulae giving the opportunity to evaluate the bandwidth of all sum resonances of the third and fourth order. Solutions of Hamiltonian's equations are obtained in the form of elliptic functions for the resonances mentioned, an estimate for the development time for the resonance is given and a scheme for calculation of the resonances of higher order is proposed