WASHINGTON -- With Democrats increasingly confident they have enough support, the House of Representatives planned for an historic vote Sunday that would enact the most dramatic changes in the nation's health care system in decades.

As a sign of that confidence -- and to quiet concerns among Democrats as well as Republicans -- House leaders Saturday abandoned a plan to approve the Senate's health care legislation without a direct vote.

President Barack Obama, in a politically charged visit to Capitol Hill, tried to rally support for the measure by telling the House's 253 Democrats to ignore the gloom-and-doom midterm election scenarios that Republican leaders and pundits have suggested if they pass the health care measure.

"You're here to represent your constituencies, and if you think your constituencies honestly shouldn't be helped, you shouldn't vote for this," Obama said. "But if you agree the system's not working for ordinary families...then help us fix this system."

"Don't do it for me. Don't do it for the Democratic Party," Obama said. "Do it for the American people."