The classical power control algorithms in wireless cellular networks have found wide applicability in attaining fixed SIR targets. This paper presents a distributed mechanism to jointly optimize SIR assignment and transmitted power in a multicellular network. Not all SIR assignments are feasible due to interference between mobile stations. We provide a new characterization of the feasible SIR region in terms of the loads on the base stations and an indication of the potential interference from mobile stations which we term spillage. Based on this characterization, we first develop a distributed algorithm that can achieve any Paretooptimal SIR assignment. Next, we pose the problem of maximizing a network-wide criterion as a utility maximization problem and present an algorithm that distributively optimizes the SIR assignment over the Pareto-optimal points. We overcome the bottleneck of centralized computation typically required for such an optimization of a network utility by exploiting the new load-spillage characterization. Extensions to power-constrained and interferenceconstrained cases are carried out. Convergence and optimality proofs as well as simulation examples using 3GPP uplink evaluation tools are presented.