Dissertation is devoted to the study of variability properties of extragalactic radio sources 3C 273, 3C 454.3, 3C 345, 3C 446, 3C 120, BL Lac, OJ 287, OT 081 at frequencies 14.5, 8 and 4.8 GHz. Basis of the study is unique data of long-term, for more than 40 years (1965 – 2011) monitoring of active galactic nucleuses, performed on the 26-m radio telescope of the University of Michigan (UMRAO). The observations from ISDC database (Data Centre for Astrophysics, University of Geneva, Switzerland) were used for quasar 3C 273 according to its long-term monitoring in radio, X-ray, ultraviolet, infrared, optical ranges from 1963 to 2007. In addition, we used data of orbital observatory RXTE (Rossi X-ray Timing Explorer) from 1996 to 2011. For the study of flux quasi-periodicity of extragalactic radio sources, full features of Fourier and continuous wavelet analysis were applied. As a result of combination these two methods the Catalog of variability periods and their properties was obtained and published. The longest and with the largest contribution to long-term flux variability periods were found in sources 3C 273, 3C 120, 3C 454.3 3C 345 (11 – 16 years) and short-term for sources BL Lac, OJ 287, OT 081 (0.4 – 1 year). The quasi-periodic changes in flux density were studied in radio, X-ray, infrared, optical, ultraviolet ranges from quasar 3C 273. It is shown that value of the primary quasiperiod in optical – X-ray diapason in range of 8 – 12 years. In X-ray range there were found quasi-harmonic components with varying periods. For the first time forecast for all investigated sources at a frequency 14.5 GHz was completed by two different methods, harmonic and autoregressive. Duration of forecasts ranged from 4 to 9 years. The best evaluation result of extrapolation for 16 years was obtained by harmonic method for source 3C 273, 3C 120. Both used method showed good correspondence between predictions and real independent observations from MOJAVE catalog from 2011 to 2015.
