DC9-30 ACFT PARKED AT GATE WITH NO COM ON ACARS HAD TO RECEIVE CLRNC FROM CLRNC DELIVERY AS WELL AS ATIS INFO. FLC EXPECTED DEP RWY TO BE VERY CLOSE TO GATE SO PREPARED FOR A SHORT TAXI; WHICH INCLUDED DOING AFTER START AND BEFORE TKOF CHKLISTS PRIOR TO TAXI. FLC RUSHED FOR AN ON TIME DEP FORGOT ABOUT THE WT AND BAL UNTIL THEY WERE TOLD AT THE DEST ARPT.

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I WAS IN COMMAND OF FLT FROM PIT TO DCA ON NOV/XX/96. AFTER AN ACFT CHANGE IN PIT; WE EXPERIENCED PROBS WITH THE ACARS SYS. WE COULD NOT RECEIVE INCOMING DATA (PDC; WX) AND HAD TO CALL FOR CLRNC. THE ORIGINAL PAX COUNT OF 46 AT 5 MINS BEFORE DEP WAS CHANGED AT THE LAST MIN BY 2 ADDITIONAL PAX. THE FO AND I DISCUSSED GIVING LOAD CTL THE NEW COUNT OF 48 (ALTHOUGH RECOGNIZING THAT AN OFF- COUNT OF 2 WAS ACCEPTABLE). WE WERE PARKED AT GATE WITH ATIS DEPS OFF RWY 10C. WE DISCUSSED THE VERY SHORT TAXI TO RWY 10C PRIOR TO PUSHBACK AND ADVISED THE FLT ATTENDANTS AS WELL. DESPITE THE LAST MIN CLOSEOUT; WE WERE ABLE TO PUSH BACK ON SCHEDULE. I DECIDED TO ACCOMPLISH BOTH THE AFTER START AND BEFORE TKOF CHKLISTS PRIOR TO CALLING FOR TAXI IN ANTICIPATION OF A SHORT NIGHT TAXI. IT WAS MY INTENTION TO BE AS FULLY PREPARED AS POSSIBLE PRIOR TO ENTERING THE TAXI ENVIRONMENT AND DEP RWY. THE TKOF DATA AND TRIM SETTINGS WERE SET ACCORDING TO THE FLT PLANNED WT ON OUR DISPATCHED RELEASE. HOWEVER; BOTH THE FO AND I ACKNOWLEDGED THAT THESE WERE ONLY APPROX FIGURES AND WOULD CERTAINLY BE UPDATED TO THE FINAL DATA RECEIVED FROM LOAD CTL VIA ACARS OR RADIO. OUR DEP RWY; HOWEVER; WAS CHANGED TO RWY 14 DUE TO NUMEROUS SBOUND FLTS AND EXPECTED DELAYS ON RWY 10C. LOAD CTL WAS CONTACTED WITH OUR COUNT OF 48. BTWN CALLS TO LOAD BY US AND OTHER ACFT; WE ACKNOWLEDGED TAXI INSTRUCTIONS; DISCUSSED THOSE INSTRUCTIONS AND PROPER TURNS IN THE COCKPIT; AND DISCOVERED THAT WE WERE IN FACT NEXT FOR TKOF ON RWY 14 (THERE WERE NO NUMEROUS DEPS AHEAD OF US). TWR CLRED US ONTO THE RWY; AND I REQUESTED THE LINE ITEMS. AT THAT MOMENT (IF NOT SOONER); WE HAD BOTH FORGOTTEN ABOUT THE FINAL WT AND BAL. NEITHER OF US REALIZED THIS ERROR UNTIL WE ARRIVED AT THE GATE IN DCA AND OPS INFORMED US ON THE RADIO AND THAT THERE WAS NO LOAD INFO FOR OUR FLT. DEPARTING WITHOUT THE FINAL WT AND BAL WAS COMPLETELY UNINTENTIONAL ON OUR PART. SEVERAL FACTORS; HOWEVER; CONTRIBUTED TO THIS SIT. THIS INCIDENT WAS PRIMARILY CAUSED BY ATTEMPTING TO GET AHEAD OF AN ANTICIPATED RUSHED DEP. ONCE WE HAD SET THE APPROX TKOF DATA; THE PROCS ERRONEOUSLY FELT AS THOUGH THEY WERE COMPLETED. THE LIGHT FUEL AND PAX LOAD DID NOT TRIGGER ANY WARNING FLAGS ASSOCIATED WITH BRIEFING HVY TKOFS. WE WERE BOTH DISTR BY THE RWY CHANGE AND OFTEN FOCUSED ON THE NIGHT TAXI. BOTH THE FO AND I HAD JUST COMPLETED 9 AND 8 DAYS RESPECTFULLY OF COMPANY BUSINESS WITHIN THE LAST 10 DAYS. THIS WAS THE LAST OF A 5 LEG DAY. FINALLY; FROM THE VERY BEGINNING OF THE FLT THE ACARS SYS PRESENTED US WITH IRREGULAR OPS AND AN INCREASED WORKLOAD. A POSSIBLE CHANGE IN COMPANY POLICY MAY PREVENT A RECURRENCE OF THIS SIT. THE ARPT ENVIRONMENT OFTEN PRESENTS CHANGING CONDITIONS WHICH DEMAND A PLT'S UNINTERRUPTED ATTN. PROBS STEMMING FROM ACARS WT AND BAL IS AN UNWARRANTED ADDITION. I BELIEVE THE BEST CORRECTIVE MEASURE IS TO MAKE THE FINAL WT AND BAL A REQUIRED COCKPIT ITEM (LIKE THE FUEL SLIP) PRIOR TO CLOSING OUT A FLT. THIS WOULD NOT ONLY ENHANCE SAFETY; BUT ALSO PREVENT BOTHERSOME CONGESTION AND DELAYS BY FLTS WAITING FOR DATA. BOTH PLTS AND ARPT CTLRS WOULD FIND THIS BENEFICIAL IN THEIR JOINT EFFORTS TO DEPART ACFT.