An M|M|N queueing system with identical servers and controlled mode, which is characterized by the parameter, “exponential distribution of service time,” is considered. The mode varies in accordance with a multithreshold strategy. The system is subjected to the action of catastrophic failures that induce the departure of all the customers from the system. An algorithm is developed for calculating the stationary state probability of the system and the performance characteristics with fixed control strategy. An optimal strategy is found numerically in a limited region of values of the threshold. Numerical examples are presented.