  We have studied a cosmological model with a cosmological term of the form
$\Lambda=3\alpha\fr{\dot R^2}{R^2}+\bt\fr{\ddot R}{R}+\fr{3\gamma}{R^2} \alpha,
\
  \bt \gamma$ are constants. The scale factor (R) is found to vary linearly
with time for both radiation and matter dominated epochs.
  The cosmological constant is found to decrease as $t^{-2}$ and the rate of
particle creation is smaller than the Steady State value.
  The model gives $\Omega^\Lambda=\fr{1}{3}$ and $\Omega^m=\fr{2}{3}$ in the
present era,
  $\Omega^\Lambda=\Omega^m=\fr{1}{2}$ in the radiation era.
  The present age of the universe $(\rm t_p$) is found to be $\rm t_p=H_p^{-1}$
, where $\rm H_p$ is the Hubble constant.
  The model is free from the main problems of the Standard Model. Since the
scale factor $\rm R\propto t$ during the entire evolution of the universe the
ratio of the cosmological constant at the Planck and present time is
$\rm\fr{\Lambda_{Pl}}{\Lambda_p}=10^{120}$.
  This decay law justifies why, today, the cosmological constant is exceedingly
small.
