AN A300 WITH SLATS EXTENDED ON APCH; OAT -8 DEGS C IN IMC WITH ONLY ENG ANTI-ICE ON; BEGAN UNCOMMANDED ROLLING. RPTR SUSPECTS AIRFRAME ICING IS THE CAUSE.

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WE FLEW DOWNWIND AT 8000 FT -8 DEGS C FOR ABOUT 10 MIN THEN DSNDED TO 4000 FT STILL IN THE CLOUDS BUT HAD SOME GND CONTACT. INTERCEPTED THE LOC AND GLIDESLOPE AT 4000 FT AND STARTED DOWN; BOTH AUTOPLTS WERE ON. THE ACFT STARTED MAKING VERY ABRUPT L AND R AILERON CTL INPUTS TO THE POINT I SUSPECTED SOMETHING WAS WRONG AS IT WAS ALSO HAVING TROUBLE MAINTAINING REF PLUS 5. I TOLD MY FO I WAS ADDING SPD TO MAINTAIN REF PLUS 10 AT LEAST AND TOOK THE AUTOPLT OFF. THE PLANE SETTLED DOWN A BIT AND I CONTINUED THE APCH. WE HAD GOOD GND CONTACT AND I HAD THE RWY 22R/L IN SIGHT BUT I WAS LNDG ON RWY 21L. THE WINDS WERE 270/15 BUT WE WERE GETTING BOUNCED AROUND PRETTY GOOD. I KNOW I HAD THE RWY IN SIGHT AND THOUGHT ABOUT TURNING ON THE WING ANTI-ICE BUT I DID NOT WANT TO TAKE THE CHANCE OF SHEDDING JUST ONE WING OF ICE AT 1000 FT; THE ENG ANTI-ICE WAS ON THE WHOLE TIME. HAND FLYING THE ACFT WAS VERY ROLL SENSITIVE BUT I LEARNED TO MAKE SMALL CORRECTIONS AND WE MADE A NORMAL LNDG. I HAD THE FLAPS AT 40 SO MAINT COULD INSPECT THEM. I WAS TOLD THE TOP OF THE WING WAS COVERED WITH 1/4 INCH OF RIME ICE WITH CLEAR ON TOP. THE RIGHT WING WAS WORSE THAN THE LEFT. FROM THE CREW DOOR I COULD SEE THE ICE OUTSIDE THE SLAT LEADING EDGE BY THE NAV LIGHT. IT STARTED AT THE LIGHT AND ROLLED BACK TO THE TOP OF THE WING. THE PNF WAS A NEW HIRE IN HIS FIRST WEEK OF IOE. HE PERFORMED ALL HIS DUTIES AND CALLS.