  We compute the effective action in terms of the Polyakov loop for the
3-dimensional pure fundamental-adjoint SU(2) lattice gauge theory at non-zero
temperatures using the strong coupling expansion. In the extended coupling
plane we show the existence of a tricritical point where the nature of the
deconfinement transition undergoes a change from second to first order. The
resulting phase structure is in excellent agreement with the Monte Carlo
results both in the fundamental and adjoint directions. The possible
consequences of our results on universality are discussed.
