CNO LCL CTLR STOPPED A C150 FROM ENTERING THE RWY MIDFIELD AND CANCELED TKOF CLRNC OF A C172 STARTING TKOF ROLL FROM THE APCH END.

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RWY 26R FULL LENGTH STANDARD DEP POINT. I HAD JUST TAKEN POS 5 MINS EARLIER ON LCL CTL; AND GND CTL COORDINATED A RWY 26R AT TXWY B DEP WITH A C150; WHICH I APPROVED. A C172 CALLED READY TO GO RWY 26R FULL LENGTH. I INSTRUCTED C172 TO HOLD SHORT RWY 26R FOR LNDG TFC; A GRUMMAN AA5. THEN C150 CALLED READY TO GO RWY 26R AT TXWY B. INSTRUCTED C150 TO HOLD SHORT OF RWY 26R; BELIEVING HE WAS A BE17 STAGGER-WING IN THE RUN-UP FOR RWY 26R FULL LENGTH. ADDITIONALLY THE PLT DID NOT READ BACK HIS HOLD SHORT INSTRUCTIONS; WHICH I FAILED TO CATCH. ALSO; I NOTIFIED C150 THAT HE WAS #2 FOR DEP; INTENDING TO DEPART THE ACFT AFTER C172 DEP. ONCE THE GRUMMAN BEGAN HIS ROLLOUT ON RWY 26R; I TAXIED C172 INTO POS FULL LENGTH. THE GRUMMAN CLRED THE RWY AND I THEN CLRED C172 FOR TKOF. BELIEVING C150 WAS THE STAGGER WING FULL LENGTH; I INSTRUCTED THE ACFT TO TAXI INTO POS AND HOLD. AS SOON AS I REALIZED WHO C150 WAS; AND WHERE HE WAS AT; (RWY 26R AT TXWY B) I IMMEDIATELY INSTRUCTED HIM TO STOP AND CANCELLED THIS CLRNC. I THEN IMMEDIATELY INSTRUCTED C172 TO CANCEL HIS TKOF CLRNC AS WELL. C150 HELD SHORT OF THE RWY AND C172 STOPPED HIS TKOF. CLOSEST PROX WAS ABOUT 2000 FT HORIZ. SOMETIMES CTLR CAN BECOME COMPLACENT IN THEIR JOB; ESPECIALLY WHEN IT IS NOT BUSY. IF I HAD PAID MORE ATTN TO THE COORD WITH GND CTL AND HAD LISTENED MORE CLOSELY TO C150'S INITIAL CALL-UP AT RWY 26R AT TXWY B; AND HAD GOTTEN A READBACK ON HIS HOLD SHORT INSTRUCTIONS; PERHAPS I WOULD HAVE RECOGNIZED THE SIT AS IT DEVELOPED AND COULD HAVE PREVENTED IT FROM HAPPENING. IT IS ALWAYS IMPORTANT TO PAY STRICT ATTN; ESPECIALLY WHEN JUST TAKING CTL OF A POS; EVEN IF TFC IS LIGHT; AS IT WAS IN THIS SIT. MAKE SURE YOU ARE AWARE OF THE TFC SIT; AND WORK YOUR TFC APPROPRIATELY AND ACCORDINGLY.