A motor-operated drive system for a window covering system including a headrail, a mechanism associated with the headrail to spread and retract the window covering, and a continuous cord loop extending below the headrail for actuating the mechanism to spread and retract the window covering. The drive system includes a motor, a driven wheel that engages and advances the continuous cord loop, and a coupling mechanism for coupling the driven wheel to a rotating output shaft of the motor for rotation of the driven wheel. The drive system includes a channel system for redirecting the continuous cord loop engaged by the driven wheel, or other mechanism for configuring the drive system so that continuous cord loop extends in a substantially vertical orientation. The coupling mechanism includes an engaged configuration in which rotation of the output shaft of the motor causes rotation of the driven wheel, and a disengaged configuration.