MD-11 FLC SET WRONG ALT IN ALT SELECT WINDOW AND OVERSHOT CLRNC ALT. CTLR INTERVENED.

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ON DSCNT TO PDX OF FLT FROM NGO (JAPAN); FLT XXX; WE WERE ON HELENS 2 ARR (HELNS2). FO FLYING (AUTOPLT ON) AND I WAS COMMUNICATING WITH ATC. WE WERE CLRED TO CROSS KALMA AT 11000 FT AND 250 KTS. I READ BACK THE CLRNC TO ZSE AND THE FO SET IN THE ALT IN THE AUTOFLT SYS. IT WAS A BEAUTIFUL DAY AND WE HAD AN EXCELLENT VIEW OF MOUNT SAINT HELENS. MADE A PA ANNOUNCEMENT TO THE PAX (ABOUT MOUNT SAINT HELENS). ZSE ASKED OUR ALT. I LOOKED AND REPLIED WE WERE LEVEL 10000 FT. ATC SWITCHED US TO PDX AND I RPTED IN LEVEL AT 10000 FT. THE FO UNDERSTOOD WE WERE CLRED TO 11000 FT; BUT MUST HAVE SET 10000 FT. I DIDN'T CATCH IT. ALSO; WE BOTH MISSED IT AGAIN AT THE 1000 FT ABOVE CALLOUT (COMPANY POLICY). SUPPLEMENTAL INFO FROM ACN 310250: COPLT WAS FLYING. I SAW HIM SET 11000 FT RESTR IN FMS AND REACH UP TO TURN ALT SELECTOR. AT THAT TIME FLT ATTENDANT CAME TO COCKPIT TO PICK UP TRAYS AND I BEGAN A PA TO PAX ABOUT MOUNT SAINT HELENS. COPLT HAD BEEN USING VERT SPD FOR DSCNT INSTEAD OF PROFILE. I DID NOT NOTICE THE MISTAKE AS I WAS DISTRACTED BY PERIPHERAL DUTIES: CABIN ATTENDANT TRAYS; IN-RANGE RPT; PA TO PAX; PLUS CABIN ATTENDANT MISSED THE STEP OUT OF COCKPIT AND DROPPED PART OF TRAYS WITH A LOUD CLATTER. 10000/11000 FT IS A KNOWN HIGH BUST ALT. I SHOULD HAVE LOOKED AT THE WINDOW TO PROVIDE BACKUP AND NOT ASSUME THE SAME ALT SET IN FMS WAS THE SAME SET IN ALT WINDOW. NOTE: COPLT WAS GIVEN THIS LEG; AS HE WAS APCHING CURRENCY DATE FOR LNDGS AND WE USUALLY COME INTO BTG; 275 DEGS; 25 MI AT 250 KIAS AT 10000 FT. BE CAREFUL OF HABITS.