LIT CTLR INTENDS TO TAXI AC50 INTO POS ON RWY 36 BUT SAYS RWY 4L. SUBSEQUENTLY THE LEARJET ON FINAL FOR RWY 4L IS INSTRUCTED TO GO AROUND TO AVOID A CONFLICT.

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I WAS WORKING THE LCL CTL POS. A LEARJET WAS ON FINAL TO RWY 4L AND AN AC50 WAS WAITING FOR DEP ON RWY 36. THERE WAS TFC XING RWY 36 SO I TOLD THE AC50 TO TAXI INTO POS AND HOLD ON RWY 36. THE LEARJET ASKED IF HE WAS CLRED TO LAND ON RWY 4L AND I SAID YES. RWY 4L AND RWY 36 COME TOGETHER AT THE END BUT DON'T CROSS AND CAN BE USED FOR ARRS ON ONE; AND DEPS ON THE OTHER AT THE SAME TIME. I WAS WATCHING THE AC50 AND HE WAS XING RWY 36 AND GOING ONTO RWY 4L. I SENT THE LEARJET AROUND AND GOT THE AC50 BACK TO RWY 36 AND CLRED HIM FOR TKOF ONCE THE RWY WAS CLR. I FELT IN THE BACK OF MY MIND THAT I HAD MISSED SOMETHING AND THE LEARJET ASKING ABOUT BEING CLRED TO LAND WAS SIGNIFICANT. I TOLD MY SUPVR ABOUT THE INCIDENT AND WE LISTENED TO THE TAPES. INSTEAD OF TELLING THE AC50 TO TAXI INTO POS AND HOLD ON RWY 36; I HAD SAID RWY 4L. THE AC50 READ BACK RWY 36 AND THE LEARJET ASKED ABOUT THE LNDG CLRNC ON RWY 4L AT ALMOST THE SAME TIME. I MISSED THE READBACK FROM THE AC50. SOMETIMES WHEN YOU LISTEN TO THE TAPES YOU CAN'T BELIEVE THAT YOU SAID WHAT YOU DID. ACFT ASK ABOUT LNDG CLRNCS ON FINAL A LOT BUT I HAD A FUNNY FEELING ABOUT THIS TIME AND IF I HAD FOLLOWED THROUGH AND MADE SURE WITH THE AC50 ABOUT RWY 36 I WOULDN'T HAVE HAD TO SEND THE LEARJET AROUND. WHEN USING RWY 36 AND RWY 4L AT THE SAME TIME I ALWAYS TRY TO KEEP A CLOSER EYE ON THE RWY END AND THE ACFT BECAUSE THERE IS ALWAYS THE POSSIBILITY OF GOING TO THE WRONG RWY BECAUSE OF THE RWY CONFIGN. I SAID THE WRONG THING; I DIDN'T CATCH THE READBACK FROM THE AC50 BUT AT LEAST I SAW THE SITUATION AND SENT THE LEARJET AROUND IN TIME TO AVOID AN ERROR. I BELIEVE THE LEARJET KNEW EXACTLY WHAT WAS GOING ON AND WOULD HAVE GONE AROUND ON HIS OWN IF I HADN'T SENT HIM AROUND. TO AVOID THIS SITUATION -- BESIDES THE OBVIOUS THING OF SAYING WHAT YOU MEAN TO SAY -- ALWAYS LISTEN FOR A READBACK AND IF YOU DON'T HEAR IT; ASK FOR IT. THE PLT READ BACK THE INSTRUCTION BUT I DIDN'T HEAR IT. I SHOULD HAVE ASKED FOR A READBACK SINCE I DIDN'T HEAR THE PLT MAKE THE FIRST ONE.