1. A method for controlling a powertrain for a hybrid electric vehicle, the vehicle having vehicle wheel brakes, the powertrain having an internal combustion engine with an accelerator pedal and a throttle controlled by a vehicle system controller that responds to accelerator pedal movement, vehicle wheel brakes, an electric motor/generator drive unit, a driver operated brake pedal for controlling regenerative drive unit braking and for applying the vehicle wheel brakes, and a battery electrically connected to the drive unit for powering the same, the method comprising the steps of: controlling engine speed and torque and drive unit speed and torque, within a maximum drive unit power capability, in response to engine throttle position whereby power values for the drive unit are within a first speed and torque operating zone characterized by high efficiency drive unit power delivery and power values for the engine are within a second speed and torque operating zone characterized by high efficiency engine power delivery; turning off the engine to effect power delivery solely by the battery; turning off the drive unit to effect power delivery solely by the engine; establishing regenerative drive unit braking power in a regenerative braking operating zone in response to driver operated brake pedal force and rate of change of brake pedal force; anticipating, upon changes in speed and torque, as brake pedal force and rate of brake pedal force change, a power limit for the regenerative braking operating zone; and applying the vehicle wheel brakes to complement regenerative braking as the regenerative braking zone power limit is approached