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.

Margarett 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. (Note: After this column was published, Ms. Campbell said she would be remaining neutral, citing state party rules that prevent its members from endorsing a candidate during a contested primary.)

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.

Trailing by more than 160 pledged delegates  those chosen in state primaries or caucuses  Mrs. Clinton has counted on superdelegates to help her overtake Mr. Obama with a late surge before the party’s convention in August. The party’s rules for proportional allocation make it highly difficult for her to erase Mr. Obama’s pledged delegate lead, even if she sweeps the final 10 contests.