OPPOSITE DIRECTION TFC; CTLR CLRED ACR X AND SMT Y FOR TKOF ON SAME RWY. POTENTIAL LTSS.

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ACR X WAS TAXIING FOR TKOF RWY 6R. HE WAS 3000-4000 FT FROM THE APCH END OF THE RWY (ON THE PARALLEL TAXIWAY) WHEN I CLRED HIM FOR TKOF RWY 6R. SMT Y CALLED READY FOR TKOF ON RWY 24L. AT THE TIME HE WAS XING RWY 24R AT GOLF TAXIWAY FOR AN INTERSECTION DEP. I CALLED S RADAR TO GET A RELEASE FOR SMT Y; AND CLRED SMT Y FOR TKOF RWY 24L. AT THAT TIME I SCANNED RWY 24L AND OBSERVED ACR X PAST THE HOLD LINES ON SUBJECT'S TAXIWAY STARTING TO ENTER RWY 6R. I CANCELLED ACR X'S CLRNC FOR TKOF. I OBSERVED SMT Y PAST THE HOLD LINES ON GOLF TAXIWAY STARTING TO ENTER 24L. I CANCELLED SMT Y'S CLRNC FOR TKOF AND INSTRUCTED HIM TO MAKE A 180 DEG TURN AND EXIT RWY 24L. WHEN SMT Y WAS OFF THE RWY I CLRED ACR X FOR TKOF RWY 6R. MY SHIFT STARTED AT 0700 LCL AND I WAS SIGNED ON POS AT 0700 LCL. THE INCIDENT OCCURRED AT 0716 LCL. WHEN SMT Y CALLED READY I SCANNED MY STRIP BOARD AND MISTOOK ACR X STRIP FOR AN ARR THAT HAD JUST EXITED RWY 6R. I DID NOT REALIZE MY MISTAKE UNTIL I SCANNED THE RWY AND CLRED SMT Y FOR TKOF. THE SITUATION WAS RESOLVED BEFORE EITHER ACFT HAD STARTED TKOF ROLL; BUT BOTH HAD STARTED TO ENTER THE RWY.