Enroute Controller declared an emergency when the aircraft indicated a fuel imbalance and requested a return to the departure airport. The reporter was later questioned regarding his actions.

Narrative

A Piper Cheyenne departed VFR; requesting his IFR [clearance]. After identifying the aircraft; a clearance was given and the Cheyenne continued his climb out. About 9;000 FT MSL; the Cheyenne called and requested to return to departure airport due to a 'pretty big fuel imbalance' and possible major fuel leak. He did not explicitly declare an emergency; however I felt as if the situation warranted it. I issued the Cheyenne a direct clearance and pilot's discretion to 6;000 FT; and further advised him that turn direction was at his discretion. I then reissued the altimeter and verified he still had the latest weather. A Developmental Controller was sitting next to me awaiting his training session and I had him advise the FLM of the situation; and that I declared an emergency for this situation. A few moments later the Cheyenne asked to leave the frequency to call the landing airport and I approved his request. At this time the training team was ready to assume the R-Side and I apprised the team of the situation and all traffic. I then moved to the D-position. The Developmental was unable to raise the Cheyenne upon further attempts and the aircraft began a descent and was lost on RADAR. From the D-position I called FSS and advised them of the situation and asked that they listen for the Cheyenne on their radios for possible information. At this time I advised another FLM that was in the area of the situation and he relayed the information to the first FLM. A few moments later; another aircraft departed and upon questioning; they stated that they saw the Cheyenne on the ground and back-taxiing on the runway.When I reported the incident to the FLM and he heard that the Cheyenne hadn't declared an emergency; it was like he tuned me out as if the fact that I felt it was an emergency didn't matter. I would suggest future emphasis on emergency situations in recurrent training for both FLMs and CPCs.