Sen. John McCain's resurgent strategy to capture independent voters in New Hampshire is forcing a flagging Rudolph W. Giuliani to scale back his efforts in the state and pin his hopes on later primaries.The Arizona senator this month swept into second place in state polls, besting the former New York mayor for the first time since July, and yesterday Mr. McCain picked up the endorsement of a former Democratic senator admired by many New Hampshire independents. "McCain's gain is Giuliani's loss; the two are tied together," said Dante Scala, a political scientist at the University of New Hampshire. "They both appeal to a somewhat more moderate Republican voter, so I think if McCain is going up, it's likely that Giuliani is drifting downward, and that's exactly what has been happening the last month."