Efficient techniques using linear programming already exist for solving the constrained power flow problem limited to the active powers only (DC-flow model). However the DC-flow approximation may not be sufficiently accurate for analyzing the security of systems with severe voltage and reactive power constraints. An iterative and decoupled method is proposed for solving the complete problem, based on the optimization of the active and reactive current injections under bus voltage and branch flow constraints. Transformer tap adjustments are also included as decision variables. The objective function is designed to accommodate security improvement as well as economical optimization, including active losses. The efficiency of this approach in computer storage and time requirement makes it a promising tool for on-line security analysis. The implementation of the method and its use for solving an actual reactive power optimization problem in an high voltage system is presented