CAPT OF A B727 TAXIED ONTO RWY TO WHICH CLRED PRIOR TO TWR INSTRUCTIONS TO DO SO WHICH RESULTED IN TWR SENDING ANOTHER ACFT AROUND WHICH WAS ON A 3 MI FINAL.

Narrative

AFTER PUSHBACK WE TAXIED FROM GATE TO RWY 17R WHICH IS A VERY SHORT TAXI. AS THE FO WAS TALKING TO GND FOR TAXI; I WAS ON THE #2 RADIO TO LOAD PLANNING; GETTING THE FINAL WTS. BECAUSE OF THIS I DID NOT COPY OUR TAXI CLRNC; BUT OBVIOUSLY WE WERE TOLD TO TAXI TO RWY 17R AND NOT CLRED ON THE RWY. AT THIS POINT I STARTED TO READ THE BEFORE TKOF CHKLIST; CONFIRM FINAL WTS THROUGH ACARS; AND TOLD THE FLT ATTENDANTS TO PREPARE FOR TKOF. ALSO AS ACTUAL WT WAS ABOVE PLANNED I HAD TO CONFIRM WE WERE STILL LEGAL FOR REDUCED PWR TKOF. AS THE ABOVE WAS BEING DONE THE AIRPLANE WAS TAXIED ONTO RWY 17R WITHOUT BEING CLRED. THE FO ASKED BOTH THE CAPT AND TWR IF WE WERE CLRED; BUT IT WAS TOO LATE AS THE NOSE OF THE ACFT WAS ON THE RWY. MEANWHILE THERE WAS AN ACFT ON A 3 NM FINAL THAT DID A GAR AS WE TAXIED CLR. BOTTOM LINE -- THE CAPT AND FO BECAME PREOCCUPIED WITH THE CHKLIST AND CONFIRMING OUR WTS AND FORGOT TO HOLD SHORT UNTIL IT WAS TOO LATE. UNFORTUNATELY DUE TO THE SHORT TAXI I WAS TOO BUSY TO CATCH THIS MISTAKE. LESSON LEARNED -- CAN'T ALLOW DISTR/FIXATION TO PRODUCE A SAFETY ISSUE.