NMAC BTWN AN MD80 CLBING ON SID DEP AND A BEECH KING AIR LEVEL 300 FT ABOVE ON A COLLISION COURSE. THE RPTR WAS RESPONDING TO A TCASII ALERT AND THEN RA WHEN ARTCC CTLR INTERVENED AND GAVE STOP CLB INSTRUCTIONS. THE KING AIR PASSED 300 FT OVERHEAD. ATC ADMITTED VIA TELECON THAT THEY HAD MADE AN ERROR.

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WE DEPARTED LAS MEAD 1 DRAKE TRANSITION. MD80 AT 126000 LBS; 140 PAX; ENRTE TUS. WE WERE ESTABLISHED ON THE BLD 108 DEG RADIAL IN IMC WHEN WE SWITCHED TO ZLA AND GIVEN FL230. THE FO WAS FLYING ON AUTOPLT. COMING THROUGH FL190 I NOTICED A TCASII TARGET ON THE GS AT 11 O'CLOCK. ONCE IT CAME ON THE SCOPE FULLY; I NOTICED IT WAS +600 FT. JUST AS I WAS MENTIONING THE TFC; ZLA TOLD US TO STOP OUR CLB AT FL190. I THEN REALIZED WE WERE ON A COLLISION COURSE WITH THE TARGET. WE WERE COMING THROUGH FL195 AND I TOLD THE FO TO DSND IMMEDIATELY AND I SPUN THE HDG KNOB 90 DEGS TO THE R AND 30 DEGS BANK TO START AN EVASIVE TURN WHILE THE FO DISCONNECTED THE AUTOPLT AND FORCIBLY PUSHED FORWARD. AT THIS POINT THE CTLR TOLD US TO TURN L; BUT WE WERE WELL INTO THE MANEUVER AND COMMITTED TO THE TURN AND DSCNT. I WATCHED THE TARGET (LATER LEARNED IT WAS A KING AIR AT FL200) COME ACROSS THE CTR OF THE TCASII AT +300 FT. ONCE WE STARTED THE EVASIVE MANEUVER; THE TCASII GAVE US THE RA TO DSND IMMEDIATELY. I DON'T KNOW HOW HIGH WE GOT BEFORE THE ACFT STARTED DSNDING. WE THEN PULLED OUT OF A HIGH SPD DIVE AT 17500 FT AND WAS THEN ABLE TO RECOMMUNICATE WITH THE CTLR. WE WERE IN THE CLOUDS THE WHOLE TIME AND UNABLE TO SEE THE TFC. THE CTLR WAS VERY APOLOGETIC AND SO WAS THE SUPVR WE TALKED TO ON THE PHONE. THEY SAID WE DID EVERYTHING RIGHT AND IT WAS A PROB ON THEIR END WHICH THEY WILL INVESTIGATE. I CREDIT THE TCASII SCOPE FOR SAVING US FROM A VERY POSSIBLE MIDAIR. I'M NOT SURE THE RA WAS QUICK ENOUGH TO SAVE US IN THIS CASE. THERE WERE NO INJURIES TO CREW OR PAX. TOO CLOSE FOR COMFORT!