ATL B727 DEP REDUCES SPD BECAUSE OF FLAP PROBS; ATC QUESTIONS CREW ACTION.

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DEPARTING ATL; RWY 8R; DURING CLEANUP HAD LEADING EDGE FLAP MALFUNCTION; ABNORMAL PROC REQUIRED ABNORMAL AIRSPD (APPROX 210 KIAS) VERSUS NORMAL AIRSPD OF 250 KIAS AS SOON AS PRACTICAL FOR OUR ACFT TYPE IN ATL. WHILE STILL ANALYZING THE PROB; ATC REQUESTED OUR AIRSPD; WE TOLD THEM 210 KIAS; AND WE WERE WORKING A FLAP PROB. ATC ADMONISHED US THAT WE SHOULD HAVE NOTIFIED HIM IMMEDIATELY OF OUR SLOW (210 KIAS VERSUS 250 KIAS) AIRSPD -- HE TOLD US WE HAD TFC BEHIND US AT 250 KIAS; AND HE GAVE US A N VECTOR OUT OF STANDARD TFC. WHILE THERE WAS APPARENTLY NO LOSS OF SEPARATION BTWN OUR ACFT AND THE FOLLOWING TFC; THE CTLR EMPHATICALLY CHASTISED US AND COMPLAINED ON THE RADIO. THE EVENTS ON DEP UNRAVELED QUITE RAPIDLY; AND OUR ATTN WAS CORRECTLY FOCUSED ON FLYING AND ANALYZING. WE HAD NOT YET GOTTEN TO THE POINT OF COMMUNICATING OUTSIDE OUR COCKPIT. THE CTLR WAS EXTREMELY UPSET; AND THIS IS WHY I AM SUBMITTING THIS NASA ASRS RPT (THE CAPT AND SO ARE ALSO SUBMITTING; AS WE ARE ALL CONCERNED ABOUT THE CTLR'S ATTITUDE; TONE; ADMONISHMENT; CRITICISM; AND LEVEL OF ANGER). THE LESSONS: THE CTLR'S WORDS DID NOTHING TO HELP OUR SIT. HE WAS UNPROFESSIONAL AND WAS A DISTR TO OUR EFFORTS. WE CAN RECONSIDER THE TIMELINESS (OR LACK OF TIMELINESS) OF OUR NOTIFICATION TO ATC. HOWEVER; 'LOW AND SLOW;' COM IN THIS CASE WAS NOT A TOP PRIORITY. NO CLR ANSWER FOR US.