Senator Barack Obama said Tuesday that if elected president he would expand the delivery of social services through churches and other religious organizations, vowing to achieve a goal he said President Bush had fallen short on during his two terms.

“The challenges we face today — from saving our planet to ending poverty — are simply too big for government to solve alone,” Mr. Obama said outside a community center here. “We need an all-hands-on-deck approach.”

Mr. Obama’s plan — his campaign said it would be the “moral center” of his administration — was unfurled against a backdrop freighted with electoral ramifications. Mr. Obama is signaling that he wants to make a push among white evangelical Protestants.