An A320 had been cleared to line up for departure on runway 23 at Adelaide. Traffic in the vicinity at that time was a VFR aircraft transiting the control zone on the coastal route to Parafield. The aerodrome controller (ADC) had decided to orbit this aircraft clear of runway 23 to facilitate the departure of the A320. Additional traffic was a Metroliner which was being sequenced to land on runway 30 at Adelaide. The ADC instructed the VFR traffic to make a right orbit, but the pilot seemed to experience difficulty in understanding the instruction and performed a left orbit. After ensuring that the take-off direction was clear the ADC cleared the A320 for take-off. At this time the Metroliner was turning onto final approach for runway 30. The investigation revealed that after being cleared for take-off, the ADC's perception was that the A320 had not moved in the expected time frame when the Metroliner reported on short finals. The ADC then cancelled the take-off clearance. The ADC's attention was divided between the orbiting aircraft, the A320 and the Metroliner. Following the landing of the Metroliner, the A320 was cleared to depart. The ADC's primary focus had been to ensure that the take-off path of the A320 was clear. His attention had been diverted by two issues, the VFR aircraft which had not followed his instruction to make a right orbit and the A320's seemingly slow reaction to the take-off clearance. Furthermore, the ADC may have misjudged the speed and distance of the Metroliner from the runway 30 threshold. However, the investigation indicated that the ADC acted quickly and in the correct sequence, cancelling the A320 take-off clearance then clearing the Metroliner to land.