  We study the mass distribution in six nearby (z<0.06) relaxed Abell clusters
of galaxies A0262, A0496, A1060, A2199, A3158 and A3558. Given the dominance of
dark matter in galaxy clusters we approximate their total density distribution
by the NFW formula characterized by virial mass and concentration. We also
assume that the anisotropy of galactic orbits is reasonably well described by a
constant and that galaxy distribution traces that of the total density. Using
the velocity and position data for 120-420 galaxies per cluster we calculate,
after removal of interlopers, the profiles of the lowest-order even velocity
moments, dispersion and kurtosis. We then reproduce the velocity moments by
jointly fitting the moments to the solutions of the Jeans equations. Including
the kurtosis in the analysis allows us to break the degeneracy between the mass
distribution and anisotropy and constrain the anisotropy as well as the virial
mass and concentration. The method is tested in detail on mock data extracted
from N-body simulations of dark matter haloes. We find that the best-fitting
galactic orbits are remarkably close to isotropic in most clusters. Using the
fitted pairs of mass and concentration parameters for the six clusters we
conclude that the trend of decreasing concentration for higher masses found in
cosmological N-body simulations is consistent with the data. By scaling the
individual cluster data by mass we combine them to create a composite cluster
with 1465 galaxies and perform a similar analysis on such sample. The estimated
concentration parameter then lies in the range 1.5 < c < 14 and the anisotropy
parameter in the range -1.1 < \beta < 0.5 at the 95 percent confidence level.
