The hill that Hillary Rodham Clinton must climb to beat Barack Obama for the Democratic presidential nomination will grow a little steeper on Monday, as it has most days lately.

Margaret Campbell, a Montana state legislator, plans to declare her support for Senator Obama, of Illinois. She becomes the 69th superdelegate he has picked up since the Feb. 5 coast-to-coast string of primary elections and caucus votes.

In the same period, Senator Clinton, of New York, has seen a net loss of two superdelegates, according to figures from the Obama campaign that Clinton aides do not dispute. That erosion may dim Mrs. Clinton’s remaining hopes even more than internal campaign turmoil, which led to the ouster on Sunday of the campaign’s chief strategist, Mark Penn.

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