IFR General Aviation pilot described an icing event when descent to lower that ATC authorized altitude was required resulting in an ATC declared emergency declaration.

Narrative

My flight was planned so as to avoid in-flight icing by flying a lower altitude (5;000 FT MSL) along VXX instead of a direct route at the flight planned (9;000 FT MSL) cruise altitude. I was VMC the entire flight and flew through two areas of light snow as I progressed toward the VOR. After passing the VOR I began to accrue clear and mixed ice in VMC conditions; I later concluded that I had encountered isolated areas of freezing rain; and requested 4;000 FT. Approximately 20 miles east of the VOR enroute to the next VOR on VXX; I informed Center that a descent to published MEA (3;200 FT) was required to escape in-flight icing. Center advised us that their minimum enroute IFR altitude was 3;700 FT. I descended to 3;200 FT and was able to escape icing for a brief time. Center informed us that this altitude (3;200 FT) required a declaration of emergency on their behalf due to the conflict in altitude minimums and that I was now an emergency aircraft. Shortly after this time I was switched to Approach Control while continuing along VXX at 3;200 FT MSL. Approach began providing RADAR vectors to Runway XXL and a descent to 3;000 FT MSL. I continued to accrue occasional clear ice the remainder of the flight. I requested as little vectoring as possible and was told I was number two for XXL. I later asked for a direct vector to the airport and was given this request and cleared for a visual approach to XXL. I made a faster than normal approach and a safe landing was made.