We propose a method for reconstructing the phase density (distribution
function) of stars in open and globular clusters based on the solutio
n of integral equations from stellar radial-velocity and proper-motion
data. The phase density is the most complete characteristic of kinema
tic and dynamical properties of clusters and the determination of even
its main features makes it possible to point out the principal relaxa
tion process that occurred in the cluster under study. We discuss vari
ous methods for extracting information on the character of the phase d
istribution of stars, in particular, for inferring the velocity anisot
ropy, from observational data. It is shown that the accuracy of modern
measurements of relative proper motions (0.0005-0.001 '' arcsec yr(-1
)) and that of correlation radial-velocity measurement methods, which
is substantially better than 1 km s(-1), are sufficient for this purpo
se.