The paper deals with tracking system design for all-wheel drive electromechanical control plant with indefinite mass-inertial characteristics, under the action of external unmatched disturbances, and with an incomplete set of sensors. To solve this problem the transformation procedure of a mathematical model of a control plant to an equivalent canonical input-output form regarding tracking errors was developed. The state variables of this form are mixed and represent functions of the state variables of the control plant, external influences and their derivatives. We developed the basic law of discontinuous feedback control and organized a sliding mode in the virtual space of mixed variables. The problem of a parametrically indeterminate matrix in front of control actions is solved by the method of hierarchy of controls. This approach ensured the asymptotic stabilization of tracking errors and the invariance of the closed system to the existing uncertainties. Under conditions of uncertainty of the input channels, synthesis procedure of the observer of the reduced order with piecewise linear correcting actions is developed for estimating mixed variables. Thus, the control and observation problems are solved with respect to the same mixed variables of the new coordinate basis