An A319 ECAM alerted GREEN SYSTEM PRESSURE LOW immediately after takeoff. While clearing the ECAM the Yellow System overheated but later cooled for normal operation. An emergency was declared and the aircraft returned to land at the departure airport.

Narrative

Incident began with a small swerve to the left around 110 KTS on take off from the runway. Captain got back on center line; but it seemed unusual. The swerve was so small you would have never have considered an abort. Climb out normal to I think 6;000 FT. ECAM for Green System LO PRESSURE. I announced ECAM. We cleared who was flying and who would accomplish ECAM. As pilot not flying I completed ECAM HYD G ENG PUMP LOW PRESS by turning off Green System Engine Pump OFF. We then looked for PTU (Power Transfer Unit) to take over the green system. I thought we had a true low pump pressure (versus a low level since we had this ECAM.) The PTU would cycle on and off. Screens cycled on and off. There was no ECAM directing to turn the PTU off because the ECAM recognized low pump pressure versus loss of fluid. We then received a HYD Y Electric Pump OVHT. We were then directed to turn off the PTU. After a couple minutes the Yellow system was restored once fluid cooled. When we lost the Yellow system; the Captain gave me the airplane and called Maintenance Control. I asked for return to the departure airport; longest runway; and equipment standing by. ATC asked about our problem and I told them souls; fuel on board and that we had lost 2 of our 3 hydraulic systems. One loss was permanent and one system was most likely going to be recovered. However since the green system was a permanent loss; we would have no nose wheel steering and have to be towed off runway. Serious issue during this event while the Captain spoke to maintenance; my conversation with ATC kept bleeding over on to the Commercial Radio. This was a serious safety concern. Very distracting to Captain and delayed our progress. I had to ask ATC to stop unnecessary conversation. I spoke to Flight Attendants and told them cabin advisory they asked about brace and evacuation signals. 'How will we know to evacuate.' Told them I would give release your seatbelts and get out; if we are in grass that's a good indication. Told them nose wheel steering was our primary concern and controllability on landing. Make sure engines have stopped if we evacuate and you guys are smart and well trained. Trust your training; you know what to do. 15 minutes till landing and everything normal at that time otherwise. Spoke to passengers. Down one system but still had 2 working fine. There would be fire trucks on landing. Noticed we were overweight still. About 144;500 LBS got out Overweight Landing Checklist for Captain and Gear Gravity Extension and sat on pedestal for him when he returned. Completed landing analysis with 1.35 landing factor only needed about 3;500 FT of runway and performance for go around 154;000. Approach check; programmed the box for return and set us up for the ILS. Extended Flaps 1 and then 2 since flap extension delayed to see how long it took and slowed to 180 KTS on downwind. Captain was now in the loop. Completed Overweight Check and then we gravity extended. He asked me to review the check for him; normal landing with minimal sink. Trucks surrounded and inspected. Tow In Checklist hard to find.