AN IMC CRJ700 ENCOUNTERED SEVERE WAKE TURB BEHIND A B747 ON APCH TO DFW BECAUSE OF IMPROPER SEPARATION BY ATC.

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WHILE ON THE APCH WE WERE TOLD WE WERE IN TRAIL OF A B747. DOING 250 KTS; THE APCH CTLR SAID; 'ACR X; 210 KTS.....DISREGARD....' IMMEDIATELY A SUPERVISOR GOT ON THE FREQUENCY AND ISSUED A 210 KT RESTR TO US. I PULLED THE THRUST LEVERS TO IDLE TO SLOW AND ASKED CAPT FOR FLAPS/SLATS 1. WE STABILIZED AT 210 KTS. ALMOST IMMEDIATELY THE ACFT STARTED LIGHTLY JUMPING UP AND DOWN. CAPT AND I BOTH MENTIONED IMMEDIATELY THAT WE THOUGHT MAYBE WE WERE GETTING CAUGHT IN THE 747'S WAKE. THE ACFT YOKE THEN WENT TO A FULL R DEFLECTION (AUTOPILOT WAS ON). THIS TRIGGERED A CAUTION SO I DISCONNECTED THE AUTOPILOT AND TOOK CONTROL. I TRIED TO STABILIZE THE ROLL RATE AND CAPT HELPED ME WITH THE RUDDER INPUTS. I PUT THE ENGINES INTO CLB THRUST BECAUSE I FEARED THAT THE SEVERE WAKE TURBULENCE WOULD INDUCE A STALL. CAPT SHOUTED FOR ME TO ROLL L OR R TO GET OUT OF IT. BECAUSE I HAD FULL R AILERON; I ELECTED TO ROLL L. THE ACFT THEN STABILIZED AND CAPT GOT ON THE RADIO AND TOLD DFW ATC ABOUT OUR ALTITUDE DEVIATION DUE TO THE ENCOUNTER. ATC NEVER SAID A WORD OTHER THAN THAT THEY STARTED GIVING US DIFFERENT VECTORS. WE ENCOUNTERED SEVERE WAKE TURBULENCE WHICH MADE THE ACFT NEARLY UNCONTROLLABLE. WE DID NOT HAVE A VISUAL OF THE 747. DFW AIR TRAFFIC CONTROL FAILED TO GIVE US PROPER SEPARATION BEHIND THE 747. DFW ATC NEEDS TO DO A BETTER JOB OF SEPARATING HEAVY ACFT FROM SMALLER ONES. THIS EVENT COULD HAVE BEEN MUCH WORSE THAN IT TURNED OUT TO BE.