AIRBUS CREW DOES NOT SET ALTIMETER TO QNH ON DSCNT NEAR BALTIMORE.

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ACR FLT. IN DSCNT PHASE WE WERE GIVEN CLRNC TO CROSS TRISH INTXN (24 MI NE OF BWI VOR) AT 12000 FT. CAPT WAS PF. CAPT NEGLECTED TO CHANGE HIS ALTIMETER SETTING TO LCL ALTIMETER OF 30.42 DSNDING THROUGH FL180. I DID NOT VERIFY THIS (PROPER XCHK) AFTER SETTING MY ALTIMETER. I WAS DISTRACTED; BUSY GETTING DCA ATIS AND SETTING UP FMS FOR APCH. I NOTICED THAT WE WERE STILL RATHER HIGH (ABOUT 12700 FT) APCHING TRISH AND I NEGLECTED TO SAY ANYTHING TO CAPT AS THIS IS NOT THAT UNUSUAL WITH THIS PARTICULAR ACFT. I WAS ALSO FIXATED ON OUR FMS PROGRESS PAGE SHOWING US BELOW OUR MANAGED VERT FLT PATH WHEN WE WERE CLRLY COMING IN TOO STEEP. BY TRISH WE WERE LEVEL AT 12700 FT (BY MY ALTIMETER) AND NO LONGER DSNDING. I WAS ABOUT TO SAY SOMETHING TO CAPT WHEN ATC QUERIED US AS TO OUR ALT. AT THAT MOMENT CAPT REALIZED HIS ALTIMETER WAS STILL SET AT STANDARD (29.92). HE CORRECTED THIS AND HE PROMPTLY DSNDED US TO 12000 FT. THE BIGGEST FACTOR IN THIS EVENT WAS IMPROPER CREW COORD IN PROPER RESETTING OF ALTIMETERS AT TRANSITION ALT. WE WERE BOTH DISTRACTED BY OTHER TASKS (CAPT BUSY MAKING CLOSE RESTR; ME ACCESSING ARR ATIS FROM ACARS). SUPPLEMENTAL INFO FROM ACN 464207: OUR DISTANCE TO TRISH REQUIRED USE OF THE SPD BRAKES IN ORDER TO MEET THE ALT XING RESTR. I DID NOT RESET MY ALTIMETER SETTING OUT OF 18000 FT DUE TO THE CONCERN OF TRYING TO MEET THE TIGHT XING RESTR. THE COPLT RESET HIS ALTIMETER BUT FAILED TO ANNOUNCE THE RESET FROM 29.92 TO 30.40. HE WAS PREOCCUPIED WITH ACQUIRING A NEW ATIS RPT. IF I DO NOT RESET MY ALTIMETER SETTING; THE QNH SETTING (AT 18000 FT) WILL FLASH ON MY PFD (PRIMARY FLT DISPLAY). UNFORTUNATELY; IF EITHER PLT RESETS HIS ALTIMETER THE OPPOSITE SIDE WITH THE INCORRECT ALTIMETER SETTING WILL STOP FLASHING. BOTH SIDES OF EACH PFD SHOULD CONTINUE TO FLASH UNTIL BOTH ALTIMETERS ARE RESET. I FEEL WE LOST AN IMPORTANT ALTIMETER SETTING REMINDER.