middle chromosphere. Our study was performed under the assumption of quasi-potential magnetic field of a single loop where its amplitude in a selected part of the current circuit of the loop varies from 30 to 100 gauss. As the main reasons for the instability development, we considered a weak large-scale electric field in a loop and slow drift motion of plasma due to the spatial inhomogeneity of its temperature and density. The identification of our solutions for the dispersion equation allowed us to determine the following. For two semi-empirical solar atmosphere models used in the calculation, MAVN F1 and MAVN F2M, the waves generated during the linear stage of instability development are kinetic Alfven waves. The distinctive features of the waves under investigation in preflare chromosphere of an active region are relatively low degree of non-isothermality of plasma which is necessary for the instability manifestation and low threshold of this instability with respect to the amplitude of subdreicer electric field in a loop �ичительными чертами исследованных волн в передспалаховій хромосфере активной области оказались относительно невысокая степень неизотермичности плазмы, необходимая для проявления неустойчивости и низкий порог этой неустойчивости по амплитуде субдрейсеровского электрического поля в петле