  The relativistic light-front dynamics (LFD) method has been shown to give a
correct description of the most recent data for the deuteron monopole and
quadrupole charge form factors obtained at the Jefferson Laboratory for elastic
electron-deuteron scattering for six values of the squared momentum transfer
between 0.66 and 1.7 (GeV/c)$^{2}$. The good agreement with the data is in
contrast with the results of the existing non-relativistic approaches. In this
work we firstly make a complementary test of the LFD applying it to calculate
another important characteristic, the nucleon momentum distribution $n(q)$ of
the deuteron using six invariant functions $f_{i}$ $(i=1,...,6)$ instead of two
($S$- and $D$-waves) in the nonrelativistic case. The comparison with the
$y$-scaling data shows the decisive role of the function $f_{5}$ which at
$q\geq$ 500 MeV/c exceeds all other $f$-functions (as well as the $S$- and
$D$-waves) for the correct description of $n(q)$ of the deuteron in the
high-momentum region. Comparison with other calculations using $S$- and
$D$-waves corresponding to various nucleon-nucleon potentials is made.
Secondly, using clear indications that the high-momentum components of $n(q)$
in heavier nuclei are related to those in the deuteron, we develop an approach
within the natural orbital representation to calculate $n(q)$ in $(A,Z)$-nuclei
on the basis of the deuteron momentum distribution. As examples, $n(q)$ in
$^{4}$He, $^{12}$C and $^{56}$Fe are calculated and good agreement with the
$y$-scaling data is obtained.
