ACFT EQUIP PROB; FAULTY PRESSURIZATION. ACFT HAD TO BE LEVELED OFF AT FL210 IN ORDER TO MAINTAIN A CABIN ALT OF 7000 FT. AFTER SOME DELAY COORDINATING WITH COMPANY MAINT AND DISPATCH; FLT WAS RETURNED TO DEP ARPT. CAPT RPTR WOULD HAVE BEEN MORE COMFORTABLE LNDG AT CLOSER ARPT; BUT COMPANY WANTED MAJOR MAINT BASE AS WELL AS EASIER HANDLING OF PAX.

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CLBING THROUGH 27000 FT I NOTICED THE CABIN ALT AT 9000 FT AND CLBING AT 500 FPM. WE BEGAN A DSCNT AND LEVELED OFF AT 21000 FT WHERE WE WERE ABLE TO MAINTAIN A CABIN ALT OF 7000 FT. I CONTACTED OUR DISPATCHER WHO IN TURN CALLED MAINT CTL AND THE DUTY OFFICER. THE DISPATCHER SAID WE DID NOT HAVE ENOUGH FUEL TO CONTINUE TO OUR DEST AT THE LOWER ALT (ORD). THEY DID NOT WANT US TO DIVERT TO ST LOUIS OR MEMPHIS FOR LACK OF MAINT. SO THE DECISION WAS MADE TO RETURN TO HOUSTON. BACK IN HOUSTON WE WOULD BE MORE ABLE TO RE-ACCOMMODATE OUR PAX AND FIX THE AIRPLANE. THE PROB WAS; THAT IT TOOK DISPATCH AND MAINT SO LONG TO MAKE UP THEIR MINDS THAT WE WERE ALMOST TO LITTLE ROCK (HALF WAY TO CHICAGO) BEFORE WE TURNED AROUND FOR HOUSTON. WE LANDED IN HOUSTON AN HR LATER WITH OVER 10000 LBS OF FUEL; WELL WITHIN SAFETY MARGIN. I UNDERSTAND THE NEED TO GET THE AIRPLANE BACK TO A MAINT CTR AND THE NEED TO TAKE THE PAX TO A PLACE WHERE THEY WOULD BE BEST ABLE TO CONTINUE THEIR TRAVEL. BUT; THINKING BACK; MAYBE WE SHOULD HAVE LANDED AT THE NEAREST SUITABLE ARPT SINCE WE REALLY DID NOT KNOW WHERE THE AIR LEAK WAS. THE POSSIBILITY OF A DECOMPRESSION WAS THERE. HOWEVER; WE DID HAVE CTL OF THE CABIN AT ALL TIMES ONCE WE DSNDED TO 21000 FT. I GUESS IT'S A JUDGEMENT CALL; BUT I TEND TO BE ON THE CONSERVATIVE SIDE. SO NEXT TIME MAYBE WE'LL DIVERT.