  Using the method of superbosonization we consider a model of a random
magnetic field (RMF) acting on both orbital motion and spin of electrons in two
dimensions. The method is based on exact integration over one particle degrees
of freedom and reduction of the problem to a functional integral over
supermatrices $Q({\bf r},{\bf r^{\prime}})$. We consider a general case when
both the direction of the RMF and the g-factor of the Zeeman splitting are
arbitrary. Integrating out fast variations of $Q$ we come to a standard
collisional unitary non-linear $\sigma$-model. The collision term consists of
orbital, spin and effective spin-orbital parts. For a particular problem of a
fixed direction of RMF, we show that additional soft excitations identified
with spin modes should appear. Considering $\delta $% -correlated weak RMF and
putting g=2 we find the transport time $\tau_{tr} $. This time is 2 times
smaller than that for spinless particles.
