NMAC BTWN AN MDT IN CRUISE AND A CLBING FIGHTER.

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WHILE ON A SCHEDULED AIRLINE FLT; WE HAD JUST LEVELED OFF AT OUR ASSIGNED ALT OF 13000 FT. THIS WAS APPROX 1000 FT ABOVE THE TOPS OF A BROKEN LAYER OF CUMULUS CLOUDS WHEN CTR ADVISED US OF TFC AT 12 O'CLOCK; INDICATING 12500 FT; UNVERIFIED. WE SAW THE TFC WHO WAS ALSO ON TCASII ABOUT 3 NM. WE OBSERVED THIS ACFT MANEUVER ABOVE AND BELOW OUR ALT APPROX 500 FT. AS THIS ACFT PASSED IN FRONT OF US FROM L TO R; WE OBSERVED THAT IT WAS MOVING AT A HIGH RATE OF SPD AND TRIED TO ASCERTAIN ITS MAKE WHEN MY FO CALLED OUT OTHER TFC AT 10 O'CLOCK AND CLOSING FROM BELOW. I SAW THIS ACFT; AN A-10 WARTHOG; LESS THAN 1/2 MI FROM US AND CLBING FROM BELOW TOWARD OUR ACFT. I DISCONNECTED THE AUTOPLT AND BEGAN AN CLB TURN FOR AVOIDANCE WHEN HE PASSED BELOW US AT APPROX 200 FT. WE HAD BEEN ABLE TO CLB ONLY 100 FT AND TURN 10 DEGS DUE TO THE SHORT REACTION TIME. THE TOTAL TIME THIS ACFT WAS IN SIGHT WAS AT MOST 5 SECONDS. IN INFORMED ZKC THAT WE HAD A NEAR MISS WITH A A-10 THAT WAS NOT THE ACFT HE HAD CALLED AS TFC. WE WERE INFORMED THAT THE ONLY TFC HE SAW WAS THE ONE ISSUED TO US. WE ALSO DID NOT SEE THE SECOND ACFT ON OUR TCASII. WE BELIEVE THAT THE SECOND ACFT WAS NOT OPERATING HIS XPONDER. WE BELIEVE THAT IF MIL ACFT ARE OPERATING AS A FLT OF MORE THAN ONE SHIP; THEY SHOULD BE IN SOME PROX TO ONE ANOTHER. THESE ACFT WERE SEPARATED BY 2 PLUS NM. AT THAT DISTANCE WE WOULD HAVE SEEN BOTH OF THEM ON TCASII HAD BOTH OF THEM BEEN OPERATING THEIR XPONDERS. TCASII IS USELESS IF BOTH ACFT ARE NOT SQUAWKING. ALSO IF THESE ACFT ARE GOING TO MANEUVER THAT CLOSE TO THE CLOUDS WHILE TRYING TO GET ON TOP; THEY SHOULD HAVE THE APPROPRIATE CLRNC TO DO SO. I HOPE THAT THIS WAS A CHANGE ENCOUNTER AND WE WERE NOT BEING PURPOSELY TARGETED FOR PRACTICE BY THE SECOND SHIP. I HAVE HAD THAT HAPPEN ON NUMEROUS OCCASIONS IN THE DISTANT PAST BY ANOTHER UNIT.