In this paper, we define labeled multigraphs with ports, a graph model which specifies connection points for nodes and allows multiple edges and loops. The dynamic evolution of these structures is expressed with multigraph rewrite rules and a multigraph rewriting relation. Then we encode the multigraphs and multigraph rewriting using algebraic terms and term rewriting to provide an operational semantics of the multigraph rewriting relation. This term version can be embedded in the rewriting calculus, thus defining for labeled multigraph transformations a high-level pattern calculus, called rho-mg calculus.