CRJ200 EXPERIENCED NEAR MISS WITH MD80 INBOUND TO ATL UNDER A80 CTL.

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WE WERE ON 180 DEG HDG; 210 KTS; DSNDING; LEVELING AT 6000 FT; A BASE LEG FOR ATL RWY 26R. AN MD80 APCHED FROM THE W; ALSO 6000 FT; ON DOWNWIND VECTOR. I DISCONNECTED THE AUTOPLT AND PREPARED TO TAKE ACTION AS MD80 WAS ABOUT 6 MI AND CLOSING. MD80 QUESTIONED ATC BEFORE WE COULD. ATC'S RESPONSE WAS THAT ATC THOUGHT WE WERE NOT DSNDING QUICKLY ENOUGH THROUGH MD80'S ALT; HOWEVER; WE WERE LAST GIVEN 6000 FT. WE COMPLIED WITH OUR RESULTANT DSCNT RA AND MD80 CLBED; RESULTING IN ABOUT 1000 FT SEPARATION AS WE CROSSED PATHS. ATC GAVE US A 120 DEG HDG; THEN 240 DEG HDG IMMEDIATELY THEREAFTER TO JOIN RWY 26L LOC. OUR RA DSCNT TOOK US TO 4500 FT. WE CLBED BACK TO 5000 FT; AFRAID TO TRY 6000 FT AGAIN; SINCE ATC SEEMED OVERWHELMED AND WE LOST VISUAL CONTACT AND TCASII INDICATION AFTER PASSING MD80. WE TRIED ASKING ATC FOR ALT DESIRED; BUT GOT NO RESPONSE UNTIL FINALLY 'CLRED FOR ILS RWY 26R' (NO ALT MENTIONED). IMPORTANT FACTORS: 1) ATL ATC USUALLY DOES A GREAT JOB; AS DO WE PLTS BASED IN ATL; BUT USING TCASII AND LOOKING OUT THE WINDOWS FOR TFC AWARENESS PREPARED US FOR THE EVENT PRIOR TO THE TCASII TA AND RA. TCASII IS GREAT FOR SITUATIONAL AWARENESS. 2) MD80 PLTS WERE ASKING 'WHO IS IN OUR PATTERN?' THIS CAUSED ATC TO ANSWER AN IRRELEVANT QUESTION VERSUS PROVIDING COLLISION AVOIDANCE INSTRUCTIONS. 3) ATC SEEMED FRUSTRATED AND NO ONE STEPPED IN TO CLEAN UP.