  We study linear power spectra and formation of large scale structures in flat
cosmological models with $\Lambda \ge 0$ and cold plus hot dark matter
components (MLM). The hot component consists of massive neutrinos with
cosmological density $\Omega_H$. The linearized Einstein-Boltzmann equations
for the evolution of the metric and density perturbations are integrated for a
set of values of the cosmological parameters. For all the considered models we
assume a scale-invariant primeval spectrum. The density weighted final linear
power spectra are normalized to the four year COBE data and have been used to
constrain the parameter space by a comparison of linear predictions with the
current observational data on large scales. The consistency of MLM predictions
with the observable data set is best obtained for models with one specie of
massive neutrinos and $\Omega_H/\Omega_M \le0.2$. For this class of MLM models
we obtain constraints from linear data on the present matter density.
Consistency with the estimated cluster abundance can be achieved for COBE
normalized MLM models with $\Omega_H/\Omega_M\le0.2$ and $ 0.45 \le \Omega_M
\le 0.75$ for $h=0.5$. If $h=0.7$ then $ 0.3 \le \Omega_M \le 0.5$. These
constraints are at $1\sigma$ level and standard MDM models are clearly ruled
out. We note that the range of allowed values for $\Omega_M$, that we obtain
for MLM models from linear analysis, is also approximately the same range that
is needed in order to consistently satisfy a variety of independent
observational constraints.
