WASHINGTON - Democratic House leaders scrambled to round up enough support yesterday for their sweeping health care overhaul, getting last-minute help from White House advisers on the eve of a historic vote scheduled for today.

Amid signs of division in the Democratic ranks, majority leader Steny Hoyer acknowledged that Speaker Nancy Pelosi and her team had yet to secure the 218 commitments needed for passage. Obama, who picked up the phone and asked fence-sitting Democrats to get on board with his top domestic priority, delayed a trip to Capitol Hill until today. Representatives were put on notice that the floor vote may be postponed until tomorrow afternoon or even early next week.

“There are many people who are still looking to get a comfort level that this is the...