B747-400 CREW WAS GIVEN 4 CHANGES IN TAXI INSTRUCTION. THE CAPT TAXIED PAST THE RWY HOLD LINE IN THE CONFUSION.

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DURING TAXI OUT; SFO GND CTL CHANGED TAXI INSTRUCTIONS 4 TIMES. DURING SOME OF THESE INSTRUCTIONS; THERE WERE BACK TAXI INSTRUCTIONS ON RWY 28L; HOLD SHORT INSTRUCTIONS (OF XING RWYS AND OF THE PLANNED TKOF RWY). NEEDLESS TO SAY; CONFUSION RESULTED AT THE HOLD SHORT LINE OF THE PLANNED DEP RWY (RWY 28R). IT SEEMED THE CAPT WAS PLANNING ON MOVING INTO POS AND HOLD AND THE FO SAID 'HOLD SHORT; I THINK.' THE CAPT STOPPED THE ACFT AND THE FO CALLED THE TWR TO CONFIRM. THE TWR SAID HOLD SHORT; WE IN THE COCKPIT HAD A DISCUSSION THAT WE MAY BE OVER THE HOLD SHORT LINE (WE COULDN'T TELL FROM THE PERSPECTIVE WELL ABOVE THE RWY). WE AS A CREW DECIDED THAT IF IT WAS IN DOUBT THAT WE WERE OVER THE LINE THAT WE NEEDED TO TELL THE TWR. WE DID. TWR SENT ANOTHER ACFT AROUND (THAT WAS ON ABOUT A 4 MI FINAL) AND WE WERE CLRED INTO POS AND SUBSEQUENT TKOF. THE SYS WORKED AS IT SHOULD; THE CREW QUERIED/ADVOCATED; THE CAPT LISTENED; AND WE ALL CAME UP WITH A PROPER DECISION ABOUT THE DOUBT ISSUE AND MADE THE PROPER ADVISORY CALL. SFO GND NEEDS TO GET THEIR 'ACT' IN ONE BAG BECAUSE OF THE RELENTLESS CHANGES AND DISTRS OF CONTINUOUSLY DIFFERENT CHANGING TAXI INSTRUCTIONS. THE REAL PROB IS THAT WE MAY HAVE BEEN CLRED INTO POS AND HOLD AND IT WAS BAD INSTRUCTIONS FROM THE TWR AND/OR GND. IT MIGHT HAVE BEEN THEIR MISTAKE; WHO KNOWS -- MAYBE; MAYBE NOT. THE POINT IS THAT THE SYS OF COM (CRM) AND A PARTNERSHIP OF WORKING WITH ATC CTLRS TO MAKE THE ENVIRONMENT SAFER IS THE MOST IMPORTANT. SUPPLEMENTAL INFO FROM ACN 616831: I BELIEVED THE CAPT HEARD THE CLRNC TO HOLD SHORT; HOWEVER; HE CONTINUED TO TAXI OVER THE HOLD SHORT LINE FOR RWY 28R. I THINK HE MAY HAVE PUT THE NOSE 8 FT BEYOND THE LINE.