A B757-200 FLC FAILS TO SET THEIR ALTIMETERS TO LCL QNH OF 29.30 FROM 29.92. THEY OVERSHOT THEIR ALT INTO THE DCA AREA.

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FLYING THE STAR INTO DCA WE WERE GIVEN A VECTOR TO PROCEED DIRECT TO OJAAY AND CROSS OJAAY AT 10000 FT; BEST FORWARD SPD. IT WAS THE FO'S LEG. I HAD GOTTEN THE ATIS AND TOLD THE FO THAT RIVER VISUALS TO RWY 18 WERE IN PROGRESS AND THE PERTINENT WINDS AND OTHER DATA. THE FO INITIATED THE DSCNT OUT OF FL220 AS WE PROCEEDED DIRECT OJAAY. DURING THE DSCNT; I GOT ON THE PA AND ANNOUNCED THE WX AND THAT WE WOULD ENJOY GREAT SCENERY AS WE SHOT THE APCH DOWN THE POTOMAC. AFTER MAKING THE PA I BEGAN TO CHK THE RIVER APCH WAYPOINTS AND ALTS THE FO HAD BUILT INTO THE FMS. AS I WAS CHKING THE FMS; WE LEVELED AT 10000 FT. SHORTLY THEREAFTER; THE APCH CTLR SAID 'FLT XY; ARE YOU IN A DSCNT?' I RESPONDED 'NEGATIVE; FLT IS AT 10000 FT ASSIGNED.' IMMEDIATELY ANOTHER VOICE CAME ON AND SAID 'CHK YOUR ALTIMETERS AT 29.30.' I KNEW RIGHT AWAY WE HAD NOT RESET THEM FROM 29.92. AS I BEGAN TO SET 29.30; THE FO INITIATED A VERT SPD DSCNT AND I SAID IMMEDIATELY; 'DISENGAGE THE AUTOPLT AND CLB.' HE DID; AND WE LEVELED AT 10000 FT WITH 29.30 SET IN A MATTER OF 5 SECONDS. THERE HAD BEEN NO TCASII ADVISORIES OR ALERTS; NOR DID I HEAR ANY COMMANDS GIVEN TO OTHER ACFT BY APCH CTL TO INDICATE A NEAR MISS OR PROB. UPON LNDG AT DCA; I CALLED APCH CTL ON THE PHONE AND RELATED MY APOLOGIES FOR CAUSING ANY EXTRA WORK AND MY THANKS FOR THEIR PROTECTING US. CONTRIBUTING FACTORS WERE BOTH THE FO AND MYSELF BEING PREOCCUPIED WITH HIS FLYING THE RIVER VISUAL WITH LITTLE EXPERIENCE ON THE B757. HE HAD BEEN ON THE ACFT SINCE DECEMBER AND NOT OPERATED INTO DCA ON IT. I KNEW HE WOULD RELY HEAVILY ON THE LNAV AND VNAV AND WANTED TO MAKE SURE HIS INPUTS WERE CORRECT. SECONDLY; THE FO AND I BOTH THOUGHT APCH CTL WANTED US AT A LOWER ALT AFTER HEARING THE PHRASE 'ARE YOU DSNDING.' THUS; THE FO'S FIRST MOVE WAS TO DSND WHEN WE REALIZED OUR MISTAKE. OBVIOUSLY; OUR INATTENTION TO DETAIL ON THE CHKLIST CAUSED THIS PROB. I ALSO BELIEVE FATIGUE WAS A FACTOR AS I HAD BEEN CALLED AT AB15 AM TO COME TO WORK THAT MORNING. SUPPLEMENTAL INFO FROM ACN 396033: AS WE LEFT FL220 THE CAPT MADE A PA TO THE PAX AND I MONITORED THE DSCNT. DUE TO A STRONG TAILWIND I EXTENDED THE SPD BRAKES FOR DRAG. AFTER THE PA; THE CAPT REVIEWED THE WAYPOINTS THAT I HAD PUT IN THE FMS FOR HELP ON THE APCH. I WAS ALSO REVIEWING THE APCH PLATE. WE NOT HAD DONE THE DSCNT CHKLIST AND ALTIMETERS WERE STILL AT 29.92. I FEEL THERE ARE SEVERAL FACTORS CONTRIBUTING TO THIS EVENT. FIRST; THE DIFFICULTY OF THE RIVER VISUAL RWY 18 APCH AND THE PROHIBITED AIRSPACE NEAR THE ARPT. SECOND; MY INEXPERIENCE WITH THE APCH AND THE CAPT'S FEELING THAT HE NEEDED TO XCHK THE FMS WAYPOINTS THAT I HAD CREATED TO ASSIST WITH THE DSCNT PROFILE. THIRD; THE STRONG TAILWIND THAT HURRIED THE DSCNT AND FINALLY THE 29.30 ALTIMETER SETTING.