The trump card Senator Hillary Rodham Clinton held in her faltering bid for president  her support among the superdelegates who can control the fate of the Democratic nomination  began slipping from her grasp on Friday as Senator Barack Obama moved into the lead on this front, with uncommitted delegates declaring their allegiance to him as others deserted her.

Mrs. Clinton publicly vowed to fight on for the nomination while campaigning on Friday in Oregon. But a new, more conciliatory tone crept into her stump speeches, as she shied away from the more spirited attacks on Mr. Obama that characterized her recent primary battles, instead engaging him more gently on the issues while aiming her fire on Senator John McCain of Arizona, the presumptive Republican nominee.

The superdelegate movement toward Mr. Obama, of Illinois  giving him a net gain of six on Friday alone, with more expected  increased the pressure on Mrs. Clinton, of New York, to at least refrain from divisive remarks, particularly after her comments on Wednesday that lower-income white voters would not support Mr. Obama if he became the Democratic nominee. Aides now say she regrets the comments.

Democratic officials said what had been a trickle of superdelegates declaring for Mr. Obama was turning into a steady stream in the wake of Tuesday’s primaries, when Mrs. Clinton lost by 14 percentage points in North Carolina and narrowly won Indiana. Mr. Obama is just 166 delegates away from the 2,025 delegates needed to secure the nomination.