  We study the dependence on $\tan\beta$ of the event kinematics of final
states with $e^+e^- /\mu^+\mu^- /e^{\pm}\mu^{\mp} + E_T^{\rm miss} + jets$, as
expected in $pp$ collisions at CERN LHC, within the framework of the minimal
supergravity model. With increase of $\tan\beta$, the third generation
sparticle masses $m_{\tilde{\tau}_1}$ and $m_{\tilde{b}_1}$ decrease due to the
increase of the tau and bottom Yukawa couplings. As a result, gluino, stop,
sbottom, chargino and neutralino decays to third generation particles and
sparticles are enhanced. With $\tan\beta$ rising, we observe a characteristic
change in the shape of the dilepton mass spectra in $e^+e^- /\mu^+\mu^-
+E_T^{\rm miss} + jets$ versus $e^{\pm}\mu^{\mp} + E_T^{\rm miss} + jets$ final
states, reflecting the presence of the decays $\tilde{\chi}_2^0\to
\tilde{\ell}_{L,R}^{\pm}\ell^{\mp}\to \tilde{\chi}_1^0 \ell^+\ell^-,
\tilde{\chi}_2^0\to \tilde{\chi}_1^0 \ell^+\ell^-$ and $\tilde{\chi}_2^0\to
\tilde{\tau}^{\pm}_1\tau^{\mp}\to \tilde{\chi}_1^0 \tau^+ \tau^-$,
$\tilde{\chi}_2^0\to \tau^+ \tau^- \tilde{\chi}_1^0$, respectively. We exploit
this effect for constraining the value of $\tan\beta$.
