  Secular and seasonal variations of the coefficient $J_2$ of the geopotential
are studied from the analysis of laser measurements of distances to the
geodetic satellites LAGEOS~1 (1988--2003) and LAGEOS~2 (1992--2003). It is
confirmed that beside the well-known annual variations with the amplitude
$\approx 2.5 \times 10^{-10}$ there also exist very significant semi-annual
variations of a comparable amplitude. Phases of these two modes are such that
the total effect may be described as a sharp postive splash of $J_2$ in August
and considerably smaller variations in the rest part of year.
