The method based on line-by-line calculations is described. In a wide spectral region for a preset accuracy, this method provides for efficient estimation of the minimum possible number of terms in the k-distribution and then determination of their parameters in order to simulate radiative fluxes and radiative cooling/heating in the atmosphere. Application of this method can significantly increase the accuracy and roughly triple the speed of current radiative blocks of climatic models based on the method of k-distribution.