  Abst\-ract: A hierarchy of effective three-dimensional theories of finite
temperature electroweak matter is studied. First an integration over non-static
modes leads to an effective theory containing a gauge field $A_{i}^{a}$, an
adjoint Higgs field $A_{0}^a$ and the fundamental Higgs field $\phi_{\alpha}$.
We carry out the integration in the 1-loop approximation, study renormalisation
effects and estimate quantitatively those terms of the effective action which
are suppressed by inverse powers of the temperature. Secondly, because of the
existence of well-separated thermal mass scales, $A_{0}^a$ can be integrated
over, and finally also $\phi_{\alpha}$, leaving an effective theory of the
$A_{i}^{a}$.In the analysis of the subsequent models particular attention is
paid to the screening of the magnetic fluctuations due to the integrated-out
degrees of freedom. Files of 2 Tables and 4 Figures are available in
(la)tex-format upon request
