A system and process for controlling propulsion and steering of a track trencher excavation machine powered by an engine includes a multiple mode propulsion and steering control system that performs a plurality of functions depending on a selection of one of a plurality of operational modes. A controller generates a vehicle propulsion hydrostatic drive signal optionally using a track drive hydraulic pressure or a track drive speed as a variable for modifying the propulsion drive signal. The controller optionally uses a hydraulic attachment drive pressure as a variable for further modifying the propulsion drive signal.