Abetted by the use of night vision goggles; helicopter pilot flies into IMC and; after encountering ice buildup; makes a slow descent to VMC and lands safely in a field.

Narrative

At XA00 we commenced our return flight. Myself in the left seat; were aided with night vision goggles. The visibility was 8-10 miles with the ceilings 1;800-2;000 FT AGL. We encountered lower ceiling around ZZZ and were proceeding south-southeast at 500 FT AGL when we lost sight of the ground and commenced inadvertent IMC procedure. We climbed to 3;500 FT MSL and after several tries; contacted Center. Center could not maneuver us until we were at 4;000 FT MSL; so we attempted to climb but were unable and the aircraft shuddered slightly when more power was applied. The windscreen became covered with ice which I reported to Center. Center suggested a VFR descent. We initiated a slow descent and at about 800 FT AGL gained ground contact with several farms/houses. I commenced a right turn; looking through the right clear portion of the windscreen. At 400 FT AGL; we had sight of a suitable landing area next to a house with a bright street light. With the aircraft searchlight and good crew coordination; we set down about 150 FT from the house without further incident.