  We calculate the relaxational dynamical critical behavior of systems of
$O(n_\|)\oplus O(n_\perp)$ symmetry including conservation of magnetization by
renormalization group (RG) theory within the minimal subtraction scheme in two
loop order. Within the stability region of the Heisenberg fixed point and the
biconical fixed point strong dynamical scaling holds with the asymptotic
dynamical critical exponent $z=2\phi/\nu-1$ where $\phi$ is the crossover
exponent and $\nu$ the exponent of the correlation length. The critical
dynamics at $n_\|=1$ and $n_\perp=2$ is governed by a small dynamical transient
exponent leading to nonuniversal nonasymptotic dynamical behavior. This may be
seen e.g. in the temperature dependence of the magnetic transport coefficients.
