CAPT OF B777-200 IS CONFUSED BY DEFERRAL OF AUTO FUNCTION OF THE HYD AIR DEMAND PUMP.

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I FLEW THE SAME AIRPLANE ON A PREVIOUS DATE. THE AIRPLANE HAD THE SAME ITEM DEFERRED IN THE SAME WAY. THE SAME DEFERRAL LANGUAGE; WHICH I BELIEVE IS WRONG AND DANGEROUS. THE DEFERRAL REQUIRES THE PLTS TO PLACE THE REMAINING ADP PUMP SELECTOR TO 'ON.' MAINT ACTION REQUIRES THE ADP WITH THE AUTO FUNCTION FAILURE TO HAVE ITS PUMP SELECTOR SWITCH IN THE 'ON' POS; IE; BOTH C1 AND C2 DEMAND PUMP SELECTOR SWITCHES WILL BE ON. THEREFORE; ONLY C1 DEMAND PUMP WILL WORK AND C2 WILL NEVER FUNCTION. DURING THE PREFLT; I REVIEWED THE RELEASE AND TRIED TO MAKE SENSE OF THE DEFERRED ITEM; DEMAND C1 HYD PUMP. THE DEFECT WAS C1 DEMAND AIR DRIVEN PUMP AUTO FUNCTION INOP. THE FLT CREW ACTION WAS WRITTEN AS FOLLOWS: FLT CREW: A) THE FOLLOWING MUST OPERATE NORMALLY: 1) REMAINING ADP (INCLUDING AUTO FUNCTION). 2) ASSOCIATED ADP ON AND OFF SELECTOR POS. B) AFTER ENG START: 1) POS REMAINING AIR DEMAND PUMP SELECTOR TO 'ON' FOR ALL PHASES OF FLT. MY QUESTION FOR MAINT CTL WAS: WHAT IS THE POS OF THE OFF/AUTO/ON SELECTOR FOR THE ASSOCIATED ADP AFTER ENG START? AFTER READING THE MAINT ACTIONS; MAINT CTL SAID THAT THE ASSOCIATED PUMP SHOULD BE ON FOR ALL PHASES OF FLT. IF C1 DEMAND PUMP SHOULD FAIL; THEN C2 WOULD TAKE OVER. I POINTED OUT THAT WITH BOTH C1 AND C2 DEMAND PUMP SWITCHES ON; THAT C2 WOULD BE DEACTIVATED AND NEVER COME ON. THIS ACTION ALSO CAUSES THE IRREGULAR PROC EICAS CAUTION MESSAGE 'HYD PRESSURE DEM C2' TO BE DISPLAYED WITH AN ICON. THE FLT CREW PROCS DO NOT TELL US TO IGNORE THE CAUTION; OVERRIDE THE CHKLIST OR COMPLETE THE CHKLIST; WHICH TELLS YOU TURN OFF C2 IF THE MESSAGE REMAINS DISPLAYED. FROM MY CONVERSATION WITH MAINT CTL PRIOR TO THE FLT; IT WAS CLR THAT BOTH C1 AND C2 DEMAND PUMPS WOULD BE ON FOR THE ENTIRE FLT. ON SEP/XA/06 PRIOR TO THE FLT BACK TO NAGOYA; I CALLED DISPATCH FROM MY HOTEL ROOM AND ARRANGED FOR A CONFERENCE CALL WITH MAINT CTL. I STILL WAS NOT SATISFIED WITH THE PROC AS WRITTEN IN THE ACFT MAINT LOG. GOING BACK OVER ALL THE GROUND THAT HAD BEEN COVERED THE PREVIOUS DAY; MAINT CTL SAID THAT THE ASSOCIATED DEMAND PUMP C1 SHOULD BE ON FOR THE ENTIRE FLT; BUT THEN IN ADDITIONAL REVIEW OF THE MAINT PROCS STATED THAT THERE ARE 3 VARIATIONS: 1) BOTH AUTO FUNCTIONS INOP (DEFERRABLE) -- 1 PUMP ON THE ENTIRE FLT. 2) 1 AUTO FUNCTION INOP (DEFERRABLE) -- ASSOCIATED PUMP ON ENTIRE FLT. 3) 1 ADP INOP (DEFERRABLE) -- REMAINING ADP SELECTOR ON THE ENTIRE FLT. MAINT CTL'S INTERP OF SITUATION #2 IS WITH 1 ADP AUTO FUNCTION INOP THAT PUMP SWITCH WILL BE TURNED ON AFTER ENG START AND STAY ON FOR ALL PHASES OF FLT AND THE REMAINING PUMP IS OPERATED NORMALLY IN THE AUTO POS. WHICH ELIMINATES THE CAUTION MESSAGE PROB; BUT WILL C2 ACTUALLY WORK IN AUTO WITH C1 POSITIONED TO 'ON.' IF THE AUTO FUNCTION DOESN'T WORK; LET'S SAY SO. THE PLT ACTIONS FOR THIS DEFERRAL; NEED TO BE WRITTEN MORE CLRLY. MY THOUGHT IS THAT IT IS AN INCORRECT PROC THE WAY IT IS WRITTEN NOW. I AGREED TO TAKE THE ACFT IF THE PUMP WAS CONSIDERED FAILED. WHICH REQUIRED MAINT TO DISCONNECT THE PUMP AND VARIOUS OTHER ACTION LISTED IN MEL. AMONG THE PLT REQUIRED ITEMS THE APU IS USED FOR AIR SOURCE FOR TKOF; RWY LIMITED IS REDUCED BY 9600 LBS AND PERFORMANCE LIMIT IS REDUCED BY 1400 LBS. I AM NOT SURE WHY; THE APU IS RUNNING THE ADP SO BLEED AIR IS NOT COMING OFF THE ENG. MAYBE THE GEAR AND FLAP RETRACTION WILL BE SLOWER WITH ONLY 1 DEMAND PUMP OPERATING. DEFERRING THE AUTO FUNCTION USING MEL; THE WAY IT IS WRITTEN; ONLY C1 DEMAND PUMP WILL OPERATE USING THE ENG AS THE BLEED SOURCE. SHOULD THERE NOT; ALSO; BE A RWY AND PERFORMANCE REDUCTION. WHAT IF THE L ENG FAILS AT V1; NOW; NO DEMAND PUMP IS OPERATING AND GEAR RETRACTION AND FLAP RETRACTION WILL BE EXTREMELY SLOW UNDER THE WORSE POSSIBLE CONDITIONS ENG FAILED AND THE GEAR DOWN. IF ADP C1 IS SELECTED ON AND ADP C2 IS SELECTED TO AUTO; THEN MAYBE THE C2 DEMAND PUMP WILL WORK. THE FLT MANUAL SAYS WITH BOTH C1 AND C2 SELECTED TO AUTO; BOTH PUMPS WILL OPERATE IF NEEDED. THE MANUAL DOES NOT ADDRESS ONE IN AUTO AND ONE SELECTEDTO ON.