In this work, a detailed analysis of the critical behavior of the Katz, Lebowitz, and Spohn (KLS) [Phys. Rev. B 28, 1665 (1983)] model is performed. This model considers a lattice gas of density rho(0) with nearest-neighbor attractive interactions between particles under the influence of an external driven field. The system is in contact with a reservoir at temperature T. The phase diagram of the KLS model is evaluated showing that it exhibits both first- and second-order phase transitions at different temperatures (T-c), depending on particle density. Ordered states are characterized by strips of high particle density running along the direction of the driving field, while disordered states exhibit gas-like behavior. A fit of the phase diagram (i.e., the T-c versus rho(0) curve) near the second-order transition is consistent with an order parameter critical exponent betaapproximate to0.33. This exponent is in agreement with an independent measurement performed by studying the dynamic evolution of the system. Furthermore, the strength of the first-order transitions is evaluated by measuring the relaxation of the system starting from both random (T-->infinity) configurations and well-ordered states (T-->0), respectively. (C) 2003 American Institute of Physics.