A B727-200 CREW; DEPARTING OKC; EXPERIENCED AN ENG PROB; PROMPTING A RETURN AND OVERWT LNDG AT OKC.

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ON OCT/THU/02; WE PLANNED TO FLY FROM OKC TO LAS. THE WX IN OKC WAS ABOUT 600 FT OVCST CEILING; 2 MI VISIBILITY WITH LIGHT RAIN; TEMP IN THE UPPER 40'S (F). AFTER ENG START; ENG ANTI-ICE WAS SELECTED DUE TO THE LOW TEMPS AND VISIBLE MOISTURE. PRIOR TO STARTING THE TKOF ROLL FROM RWY 35L; PWR WAS ADVANCED TO 70% N1 FOR 15 SECONDS FOR ANTI-ICE CONSIDERATIONS; THEN TKOF THRUST WAS SET TO 2.20 EPR ON ALL 3 ENGS. AFTER TKOF AND DURING FLAP RETRACTION; THE FE NOTICED THAT #2 EPR HAD DROPPED TO 1.6 AND NOTIFIED THE REST OF THE CREW. THE CAPT NOTIFIED OKLAHOMA CITY DEP THAT WE REQUESTED TO MAKE A PRECAUTIONARY LNDG. THEY ASKED IF WE WERE DECLARING AN EMER AND THE CAPT REPLIED 'NOT AT THIS TIME.' THIS IS BECAUSE WE WEREN'T SURE IF WE HAD AN ACTUAL ENG PROB OR AN INDICATION PROB. AFTER XCHKING ALL OF THE OTHER ENG INSTS AND VERIFYING THAT ENG ANTI-ICE WAS ON AND OPERATIONAL; IT WAS DETERMINED THAT WE DID HAVE AN ENG PROB AND THAT A PRECAUTIONARY LNDG BACK AT OKC WAS INDEED THE BEST COURSE OF ACTION. THE FE ASKED THE CAPT IF HE WANTED TO DUMP FUEL IN ORDER TO ATTAIN OUR MAX LNDG WT; WHICH IS 160000 LBS. WE WERE CURRENTLY AT ABOUT 172000 LBS. I (FO) CHKED THE LNDG PERFORMANCE NUMBERS FOR THE RWY OF INTENDED LNDG AND ADVISED THE CAPT THAT LNDG COULD BE MADE UNDER THE CURRENT CONDITIONS UP TO 190000 LBS. THE CAPT DECIDED NOT TO DUMP FUEL; PRESUMABLY BECAUSE OF THE BAD WX; AND DECIDED TO DO AN OVERWT LNDG. I CONTINUED TO FLY THE ACFT AND MADE AN ILS APCH TO RWY 35R WITH A NORMAL TOUCHDOWN AND LNDG AT 170000 LBS. WE CLRED THE RWY AND TAXIED BACK TO THE GATE. WHAT WE FAILED TO DO AS A CREW IS DECLARE AN EMER. THEREFORE; WE BROKE THE FAR'S AND COMPANY POLICY BY LNDG OVERWT WITHOUT DECLARING AN EMER. I BELIEVE THAT BECAUSE THERE WAS SOME CONFUSION INITIALLY AS TO WHETHER OR NOT WE ACTUALLY HAD AN ENG PROB; WE DELAYED DECLARING AN EMER. WE HAD TO ACCOMPLISH A LARGE NUMBER OF TASKS (CHKLISTS; SETTING UP AND BRIEFING THE APCH; ETC) IN A SHORT AMOUNT OF TIME (WE WERE IN THE AIR ONLY ABOUT 15 SECONDS). AS THE SIT UNFOLDED; WE GOT SO WRAPPED UP IN GETTING THE ACFT BACK DOWN ON THE GND SAFELY THAT WE SIMPLY FORGOT TO DECLARE AN EMER.