When distracted by maintenance activity the flight crew of a B757-200 failed to complete their review of the PDC clearance and missed the revised SID. A track deviation following takeoff illuminated the failure and ATC recleared them along with a cautionary remonstration to be more careful in the future.

Narrative

Captain programmed FMS; and I verified. Flight plan called for the TRALR 4 departure DVC transition. TRALR 4 departure off of Runway 25R is a left hand turn out. I requested and printed out the PDC. At this time; two mechanics arrived to check a lavatory problem. I had just begun to look at PDC and put 19;000 FT into Alt Window when the Captain went into cabin to confer with the mechanic in the cabin. A second mechanic was in cockpit working on the paperwork and asked for the Logbook. I asked what was wrong with the aircraft. He told me the mid-aft lavatory was leaking. I asked if they were going to defer it. This distracted me from the PDC and; as I continued the conversation with the mechanic; I disregarded the PDC. After the mechanics completed the paperwork the Captain returned to the cockpit and we checked the logbook; completed the Pushback/Start Checklist; and called for pushback.Everything was normal from here on out until after takeoff; when Departure Control said something to the effect of; 'You are flying the TRALR 4 departure and were assigned the STAAV 4 departure. There is no traffic so it's not a problem but; during the day; that would be a Pilot Deviation.' The STAAV 4 departure has a right hand turn out off of Runway 25R. As soon as I heard those words I realized I had only verified the Initial Altitude on the PDC when I had been distracted. I never came back to the PDC.In order to prevent a recurrence of this type of mistake; check; re-check; and check a third time; especially when the flight departs at a late time for your body clock. While I had rested; what I presumed to be an adequate amount of time; I am sure the late departure had some to do with my mistake. We were scheduled to push at a time frame when I am usually asleep. Distractions cannot be fully eliminated; but we can minimize the negative consequences of these distractions by checking and re-checking before push back.