The linear electro-optic effect in LiNbO3 has been investigated in the wavelength range from 0.4 to 1.15 mu m at applied field frequencies of 200 Hz and 9.45 GHz. The dispersion of clamped (rs22) and unclamped (r22T) electro-optic coefficients is measured. The values of the clamped electro-optic coefficients (rs22) are determined. Based on the results of measurements and reported data of the second harmonic generation coefficient, an attempt has been made to estimate the value and dispersion of the electronic and ionic contributions to the clamped electro-optic effect.