A power transmission has an internal combustion engine and motor/generators which are combined through a summing planetary gearing. The planetary gearing cooperates with downstream gearing to provide a hybrid power transmission. A plurality of auxiliary or power take-off (PTO) shafts are included to permit the operation of auxiliary devices, such as main hydraulic pumps, air conditioners or power steering pumps. A fluid operated clutch is incorporated between the engine and the gearing so that the motor/generators can drive the PTO shafts independently of the engine. The main pump fluid output can be directed to engage the clutch when the engine input is desired. The motor/generators are controlled to provide output speed resulting in one member of the gearing being driven at a speed equal to the idle speed of the engine, such that the clutch can be synchronously engaged.