NMAC BTWN A PIPER PA32 IN LEVEL FLT AT 2800 FT MSL AT AN INTXN OF 2 VICTOR AIRWAYS; AND A C172 DSNDING AND XING IN FRONT OF THE PA32 ON THE XING AIRWAY. BOTH ACFT WERE ON ATC FLT FOLLOWING.

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ON A VFR FLT FROM PTW TO IPT AT 2800 FT; V164; 324 DEG RADIALS; ALLENTOWN APCH GAVE ME ADVISORIES TO THE END OF THEIR AIRSPACE. ALLENTOWN THEN ADVISED ME TO SQUAWK 1200 AND CALL AVP APCH IN 5 MINS. IT WAS EXACTLY XA25 AT THAT TIME. AT XA30 I CALLED AVP APCH. I WAS TOLD TO SQUAWK 1200 AND IDENT. DID NOT HEAR BACK FOR SEVERAL MINS. FINALLY; AVP CAME BACK AND TOLD ME HE MISSED MY IDENT AND WOULD I DO IT AGAIN. WHILE IN THE PROCESS OF GIVING ME A SQUAWK CODE; MY COPLT POINTED OUT THE CESSNA AT MY 10 O'CLOCK POS; DSNDING DIRECTLY ACROSS MY PATH. WE WERE NO FURTHER THAN 50 FT APART! AFTER I GATHERED MYSELF; I ASKED AVP IF HE HAD US ON HIS SCREEN. INSTEAD OF ANSWERING ME; THE CTLR ASKED THE CESSNA IF HE HAD SEEN ME. THE CESSNA REPLIED 'NOT UNTIL I WAS ON TOP OF HIM.' I THEN ASKED AVP IF HE HAD US ON HIS SCREEN. THERE WAS A PAUSE; AND THEN HE CAME BACK; 'YOUR XPONDER IS INTERMITTENT.' THE CTLR NEVER ANSWERED MY QUESTION. MINS LATER; HE HANDED ME OFF TO ZNY AND THE FLT WAS UNEVENTFUL FOR THE REMAINING TIME TO WILLIAMSPORT. AT NO TIME BEFORE OR AFTER THIS FLT HAS ANY CTLR EVER SAID MY XPONDER WAS NOT WORKING CORRECTLY. THERE WAS NO TIME FOR EVASIVE ACTION. HAD WE CROSSED PATHS 50 FT CLOSER; I WOULD NOT BE WRITING THIS. IT IS ONLY BY THE GRACE OF GOD WE ARE STILL HERE. MY EYES WERE DIVERTED WHEN TUNING IN THE XPONDER. I CANNOT EXPLAIN THE CESSNA'S EYES; BUT WHERE WERE THE CTLR'S EYES? DID HE HAVE US ON HIS SCREEN OR NOT?