ALTDEV ALT EXCURSION IN ICING CONDITIONS.

Narrative

DURING CRUISE FLT AT FL200 120 NM OUT OF EWA 234 DEGS ON A FLT FROM ATL TO GTR; WE ENCOUNTERED SEVERE ICING. ATC ADVISED US TO RERTE FROM VUZ TO MEI FOR WX. WE WERE IN THE PROCESS WHEN WE STARTED PICKING UP ICE. WE TURNED ON ALL ICE PROTECTION AND PLANNED A DSCNT AND A TURN N AT MEI. ICE STARTED TO INCREASE TO ABOUT AN INCH WHEN I NOTICED A DECREASE IN AIRSPD FROM 180 KTS TO 140 KTS AND MAX CRUISE WAS ALREADY APPLIED. I ASKED THE FO TO CALL ATC AND TELL THEM WE NEEDED LOWER. WITH NO PWR LEFT AND THE ACFT AT VREF; A STALL BUFFET STARTED. I WAS FORCED TO START DSNDING WITHOUT AN ATC CLRNC DESPITE OUR ATTEMPTS TO CALL. WE HAD DSNDED TO 19500 BEFORE MAKING CONTACT AND RECEIVING 12000 FT FROM ATC. THE ICE HAD GROWN TO 2 INCHES AND IT ONLY TOOK 30 SECONDS FOR THE INCIDENT TO OCCUR AND ATC RESPONDED BEFORE I COULD SQUAWK 7700. I WAS MORE CONCERNED WITH THE ADVANCED STALL SIT THAN WITH THE CLRNC; AND THE FO WAS OCCUPIED WITH THE ICE BOOTS AND THE CHATTER ON CTR FREQ TO CHANGE SQUAWK CODES. WITH AN OUTSIDE AIR TEMP OF ONLY -5 DEGS C AND THE LACK OF HVY PRECIPITATION; I WAS SURPRISED AT HOW FAST THE SIT DETERIORATED.