  We study the contribution of a stochastic background (SB) of primordial
magnetic fields (PMF) on the anisotropies in temperature and polarization of
the cosmic microwave background radiation (CMB). A SB of PMF modelled as a
fully inhomogeneous component induces non-gaussian scalar, vector and tensor
metric linear perturbations. We give the exact expressions for the Fourier
spectra of the relevant energy-momentum components of such SB, given a
power-law dependence parametrized by a spectral index $n_B$ for the magnetic
field power spectrum cut at a damping scale $k_D$. For all the values of $n_B$
considered here, the contribution to the CMB temperature pattern by such a SB
is dominated by the scalar contribution and then by the vector one at higher
multipoles. We also give an analytic estimate of the scalar contribution to the
CMB temperature pattern.
