Optimal multilevel feedback control policies for rate based flow controlin available bit rate (ABR) service in asynchronous transfer mode (ATM)networks are obtained in the presence of information and propagationdelays, using a numerically efficient two timescale simultaneousperturbation stochastic approximation (SPSA) algorithm. Convergenceanalysis of the algorithm is presented. Numerical experiments demonstratefast convergence even in the presence of significant delays and largenumber of parametrized policy levels.