  A perturbation method is presented which can be applied to the description of
a wide range of physical problems that deal with dynamics of dipolar coupled
spins in solids. The method is based on expansion of the operator exponent in a
perturbation series. As example of application the method, the multile-quantum
coherence dynamics in three and four spin cluster are considered. The
calculated 0Q- and 2Q intensities vs the duration of the preparation period
give closed agreement with exact results and simulations data. The exact
solutions for J0Q and J2Q coherences in four spin system are obtained.
