  A field-theoretic approach is applied to describe behavior of homogeneous
three-dimensional systems with long-range interactions defined by two order
parameters at bicritical and tetracritical points. Renormalization- group
equations are analyzed in the two-loop approximation by using the Pade-Borel
summation technique. The fixed points corresponding to various types of
multicritical behavior are determined. It is shown that effects due to
long-range interactions can be responsible for a change from bicritical to
tetracritical behavior.
