AN A320 PLT RPTS EXCESSIVE ROLL RATE DURING LNDG FLARE CAUSED 1 MAIN GEAR TO TOUCH DOWN DURING GAR IN STRONG XWIND.

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FO WAS PF FOR THIS LEG. WINDSHEAR ADVISORIES IN EFFECT AT IAD. TWR WIND WAS 320 DEGS AT 20 KTS GUSTING TO 35 FLAPS. FLAPS 3 DEG LNDG FOR RWY 1L. APCH AND FLARE WERE NORMAL WITH FO USING GOOD XWIND TECHNIQUE. IN FLARE; THE L WING DROPPED QUICKLY TO THE POINT THAT I WAS CONCERNED WE MIGHT SCRAPE THE WING SAIL; SO I ORDERED A GAR. PART OF MY CONCERN WAS THAT IT WAS IMPOSSIBLE TO SAY WHETHER WING DROP WAS CAUSED BY INTERNAL OR EXTERNAL EVENTS DUE TO NO BACK DRIVE AVAILABLE ON AIRBUS FLT CTL SYS EXCEPT FOR RUDDER INPUTS. I FELT SAFEST ACTION WAS TO ABANDON LNDG AND TRY AGAIN. WE DISCUSSED THE EVENT ON DOWNWIND LEG AND A NORMAL LNDG WAS MADE ON RWY 1R USING FLAPS 3 DEGS AGAIN. I AM NOT CONVINCED THAT RECOMMENDED PROC OF USING FLAPS 3 DEGS IS BEST SINCE HIGHER ROLL RATES ARE APPARENT IN THIS CONFIGN; WHICH MAY OR MAY NOT HAVE CONTRIBUTED TO EVENT. I AM STILL UNSURE AS TO CAUSE OF EXCESSIVE ROLL; WHICH IS MY GREATEST CONCERN RIGHT NOW. I ASKED MAINT TO INSPECT ACFT AFTER LNDG TO ENSURE NO DAMAGE APPARENT (THE L MAIN GEAR TOUCHED DOWN DURING THE GAR). THE COPLT IS A HIGHLY EXPERIENCED FO AND I DID NOT SEE OR FEEL HIM USE ANY TECHNIQUES THAT I THOUGHT WERE INAPPROPRIATE FOR THE CIRCUMSTANCES. I FEEL THAT 'ROTOR' TURB OFF THE TRESS ADJACENT TO THE RWY MAY HAVE BEEN A FACTOR. HISTORY HAS SHOWN THAT THIS KIND OF SURFACE WIND AT IAD PRODUCED UNDESIRABLE SURFACE FRICTION EVENTS ON RWY 1L.