The objective of this research is to develop an analytical approach to control two-time-scale systems operating under certain noise parameters. This approach addresses two important design criteria: augmentation of large-scale system with disturbance model and its two-time-scale representation, and order reduction of the large-scale systems for reduced controller design complexity. The problem of large-scale system with Gaussian noises is solved as the stochastic system implementing linear-quadratic Gaussian control. Order reduction method uses singular perturbation techniques for the simplicity of control algorithms. Control law design process for a singularly perturbed stochastic system includes implementation and comparative analysis of optimal, composite, and reduced controller techniques. Practical model, longitudinal dynamics of digital fly-by-wire F-8C fighter aircraft, illustrates the validation of the proposed concepts.