A B737-400 PIC RPT ON THE CONFUSION CREATED BY IMPROPER CHART AND APCH CTLR PHRASEOLOGY FOR AN IAP LOC DME APCH AT LGA; NY.

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ATIS FOR LGA STATED 'ILS TO RWY 13.' APCH CLRED US FOR AN 'ILS DME TO RWY 13; GS OUT.' THE PROB WITH THIS APCH PLATE IS THAT THERE IS NO SUCH THING AS A 'DME' ILS FOR RWY 13. THERE IS; HOWEVER; AN ILS LOC APCH PROC WITH A 500 FT MDA IF THE 2.8 IGDA FIX IS AVAILABLE AND A 800 FT MDA WITH NO DME. THE PLATE SHOWS 1800 FT FROM STEED IN BOLD PRINT AND IN NON BOLD PRINT AN 800 FT PROFILE TO 2.8 DME. WHEN A CLRNC IS RECEIVED FOR A DME ILS; GS OUT; THIS CREATES A BIT OF CONFUSION. MANY ACFT ON FREQ WERE QUESTIONING THE CLRNC; AND IT DEFINITELY CREATED CONFUSION FOR US TOO. WE INTERPED THIS AS 1800 FT TO 5.7 DME THEN A DSCNT NO LOWER THAN 500 FT UNTIL AFTER 2.8 DME. I BEGAN THE STANDARD 1000-1200 FPM DSCNT AT 5.7 MI AND WAS SOMEWHERE BTWN 500-800 FT AT APPROX 2.8 IGDA ILS. WE REALIZED; AFTER THE FACT; THAT 800 FT IS THE INTENDED MINIMUM ALT UNTIL AFTER 2.8 MI. WE DIDN'T RING ANY LOW ALT ALARMS AT APCH; TWR OR GPWS; SO THE DSCNT WAS NO DOUBT SAFE. BUT; THIS IS AN UNCOMFORTABLE SIT WITH AN AMBIGUOUS CLRNC; AND AN APCH PLATE THAT NEEDS REFINEMENT IF APCH IS GOING TO CLR ACFT FOR AN ILS DME. NEXT TIME; I DEFINITELY WOULD ASK FOR CLARIFICATION; BECAUSE BOTH MY FO AND MYSELF INTERPED THE CLRNC AND PLATE IN THE SAME MANNER EVEN AFTER A VERY THOROUGH APCH BRIEFING. IT WAS ONLY SOME TIME AFTER THE APCH WHEN WE WERE DISCUSSING THE CLRNC AND THE CTLR'S INTENTIONS; AND THE PLATE'S AMBIGUITY THAT WE REALIZED THAT 800 FT WAS ACTUALLY THE MINIMUM ALT AT 2.8 MI -- NOT 800 FT TO 500 FT. 500 FT IS REALLY INTENDED TO BE DSNDED TO AFTER 2.8 MI. A FURTHER CLARIFICATION WITH THE CTLR WOULD; NO DOUBT; HAVE RAISED A 'RED FLAG' TO BRING THE ACTUAL INTENT OF THE PLATE TO THE SURFACE. LATER INVESTIGATION OF SIMILAR PLATES REVEALED VERY FEW THAT WERE SIMILAR; AND IN ALL CASES; THE HIGHER OF THE 2 MDA'S WAS PRECEDED BY A SIGNIFICANTLY HIGHER LEVELOFF ALT PRIOR TO DSCNT TO EITHER OF THE 2 MDA'S. THIS IS GOOD BECAUSE IT CALLS ONE'S ATTN TO LEVELING OFF AT AN ALT ABOVE BOTH MDA'S BEFORE FINAL DSCNT IS STARTED. AT LGA; 800 FT IS THE INTERMEDIATE AND THE FINAL ALT FOR ONE MDA; WHILE THERE IS STILL A LOWER 500 FT MDA. THIS IS DEFINITELY NOT A DME ILS GS OUT APCH AND IS NOT PARTICULARLY 'USER FRIENDLY' EITHER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT STATED THAT HE HAD NOT RPTED THIS INCIDENT TO HIS COMPANY OR THE FAA. HE IS LOOKING FORWARD TOWARDS RETIREMENT WHICH IS A VERY SHORT TIME AWAY. HE AGREED WITH THE ANALYST THAT THERE SHOULD BE 2 APCH PLATES CREATED; 1 FOR EACH APCH; FULL ILS AND THE LOC APCH.