  We consider the regions of the MSSM parameter space where the top squarks
become light and even may be the LSP. This happens when the triple scalar
coupling A becomes very big compared to m_0. We show that in this case the
requirement that the LSP is neutral imposes noticeable constraint on the
parameter space excluding low m_0 and m_{1/2} similar to constraint from the
Higgs mass limit. In some cases these constraints overlap. This picture takes
place in a wide region of \tan\beta. In a narrow band close to the border line
the stops are long-lived particles and decay into quarks and neutralino
(chargino). The cross-section of their production at LHC via gluon fusion
mechanism in this region may reach a few pb.
