FLC OF AN MLG ACR ACFT UNDERSHOT CLB ALT BY LEVELING OFF FOR LOSS OF ACFT CABIN PRESSURE. FLT SUBSEQUENTLY RETURNED FOR LNDG.

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AT 10000 FT MSL; THE 'CABIN ALT MASTER WARNING' LIGHTS ILLUMINATED WHILE WE WERE CLBING TO 17000 FT. I LEVELED THE ACFT AT 10000 FT AND ADVISED DEP CTL OF OUR LEVEL OFF. SIMULTANEOUSLY; THE CABIN ATTENDANT CALL LIGHT AND CHIME WAS ACTIVATED FROM A FLT ATTENDANT LOCATED AT THE AFT EXIT DOOR AND AFT GALLEY AREA. HE ADVISED US THAT THERE WAS A SUBSTANTIAL AIR LEAK AT THE AFT GALLEY SVC DOOR. A JUMP SEAT RIDER (WHO WAS ALSO A QUALIFIED PLT FLYING FOR THE SAME COMPANY); WAS ASKED TO GO TO THE BACK AND SURVEY THE DOOR. MEANWHILE; THE CAPT USED HIS QRH TO ATTEMPT TO CORRECT A LOSS OR LACK OF CABIN PRESSURE (WE HAD '0' DIFFERENTIAL). THE JUMP SEAT RIDER RETURNED TO THE COCKPIT EXPLAINING THAT THE AFT GALLEY SVC DOOR WAS LEAKING; QUITE A BIT. THE CAPT CONTINUED QRH PROCS TO ATTEMPT TO PRESSURIZE THE ACFT AND ALSO CALLED ACR MAINT AND FTW DISPATCH IN AN EFFORT TO GET SUGGESTED IDEAS/OPINIONS. I CONTINUED TO FLY THE ACFT AND GOT US AN INITIAL CLRNC W; TOWARD TUCSON AT 10000 FT. WE WERE UNABLE TO PRESSURIZE THE ACFT AND WITH EVENTUAL AGREEMENT FROM ACR MAINT AND FTW DISPATCH; THE DECISION WAS MADE TO RETURN TO DFW. (WX ENRTE TO TUCSON WAS VERY HVY!) AN UNEVENTFUL 40 FLAP OVERWT LNDG AT DFW WAS MADE BY THE CAPT. WT AT LNDG WAS APPROX 138800 LBS (MAX LNDG WT IS 130000 LBS). THE LNDG AND ROLLOUT WERE SMOOTH AND UNEVENTFUL. (THE GALLEY DOOR WARNING LIGHT WAS OPERATIVE BUT DID NOT INDICATE AN OPEN DOOR.)