Following a Go Around; an Air Carrier crew declared a fuel emergency because ATC requested they go around again. The aircraft's light weight and slow speed created a traffic consideration for ATC.

Narrative

While on radar vectors for final approach; and after just completing a go around from that same runway; we were on an assigned heading to intercept final; expecting a visual approach. The Controller requested our airspeed and I responded by stating it was 150 KTS. The Controller then issued a heading and altitude to break us off the approach. I stated that we would not be able to do that we must land due to low fuel. The Controller then asked if I was declaring a low fuel emergency and I stated yes. Fuel onboard at that time was 7500 LBS. We had just completed a turn around the pattern from a previous missed approach and I was forced to make a split second decision whether or not another missed approach with an unknown traffic sequence was safe with the amount of fuel remaining. I concluded it was not and choose to declare the low fuel emergency based on the circumstance at that time. We made a safe landing and taxied to our gate. Fuel remaining at the gate was 6900 LBS; two thousand pounds below our plan of 8900 LBS. Contributing factors: Last assigned airspeed by approach was 190 KTS on downwind. We were turning final. We were not told to maintain that speed or any other speed as we were vectored to final approach. The aircraft gross weight was low with a Vref speed of 119 KTS. In order to configure the aircraft for landing and be in a position at 1000 FT AFL to made a normal approach and landing it was necessary to start slowing the aircraft. I should have notified the Controller of our speed reduction; however I thought it was evident to him.