  A procedure to solve few-body problems is developed which is based on an
expansion over a small parameter. The parameter is the ratio of potential
energy to kinetic energy for states having not small hyperspherical quantum
numbers, K>K_0. Dynamic equations are reduced perturbatively to equations in
the finite-dimension subspace with K\le K_0. Contributions from states with
K>K_0 are taken into account in a closed form, i.e. without an expansion over
basis functions. Estimates on efficiency of the approach are presented.
