In the framework of the model with string fusion and the formation of string clusters the correlations between multiplicities in two separated rapidity windows in pp collisions at LHC energies were studied and the results obtained were compared with data from the ALICE collaboration at CERN. The simulation is carried out within the framework of a Monte Carlo implementation of the colour quark-gluon string model. String fusion effects are taken into account by implementing a finite lattice in the plane of the impact parameter. The dependence of the correlation coefficient between multiplicities in two rapidity observation windows on the distance between these windows is calculated for four values of their width and three values of initial energy. It is shown that the model with string clusters describes the main features of the behavior of the correlation coefficient: its increase with increasing initial energy, decrease with increasing rapidity distance between observation windows, and nonlinear dependence on the width of the rapidity window.