WASHINGTON — After a frenzied last push to nail down final commitments and resolve lingering disputes in their ranks, House Democrats are poised today to pass the most sweeping change to the nation's health care system since the creation of Medicare nearly 50 years ago.

President Obama exhorted Democrats yesterday to stay true to their party's legacy and make history by bringing health insurance to millions of struggling families now left out. Today's vote is scheduled to begin at 7 a.m. Hawai'i time.

The 10-year, $940 billion health care package is expected to extend medical insurance coverage to 32 million people by 2019, while also using a series of tax hikes and cuts in Medicare spending to reduce the overall federal deficit by $138 billion over the next decade, according to a preliminary estimate by the nonpartisan Congressional Budget Office.

Obama yesterday invoked Abraham Lincoln's moral compass and extolled Democratic achievements such as Social Security and Medicare on a day marked by a frenetic hunt for votes inside the Capitol and angry tea party demonstrations at the door.

"Is this the single most important step that we have taken on health care since Medicare?" Obama asked rank-and-file Democrats. "Absolutely. Is this the most important piece of domestic legislation, in terms of giving a break to hard working, middle-class families out there since Medicare? Absolutely.

"It is in your hands," Obama said. "It is time to pass health care reform for America and I am confident that you are going to do it tomorrow."

In an appeal to unity ahead of a career-defining vote, Obama and House leaders were joined by Senate Majority Leader Harry Reid, D-Nev., who brought a pledge from more than 50 of his Democratic colleagues to promptly finish the bill after the House votes today. House Democrats have been wary of being left in the lurch by the Senate.

Barring a last-minute breakdown over abortion, House Democrats are now expected to have the 216 votes they need to pass the package. The New York Times reported they had 206 of the 216 votes, with 21 Democrats still undecided, many because of their opposition to abortion.

A series of last-minute flare-ups threatened to slow the Democrats' march to passage, after more than a year of grueling effort.

The most intense focus was on a small group of Democrats concerned that abortion funding restrictions in the legislation don't go far enough. Determined to avoid votes on such a charged issue, Democratic leaders raised the possibility of addressing the concerns of abortion foes through an executive order from Obama. It would reaffirm existing federal law barring taxpayer funded abortions except in cases of rape, incest or to save the life of the mother.

House Democratic leaders abandoned a much-challenged procedure for passing the legislation after an outcry from Republicans and protest from some of their members. According to the new plan, the House will vote up or down the health care bill passed by the Senate on Christmas Eve as well as a package of changes.

The Senate bill would then go to Obama for his signature and the companion measure to the Senate, which hopes to pass it within the week.

Minutes after the leadership's change of heart, Rep. Dennis Cardoza, D-Calif., announced his support for the health care legislation. Cardoza had criticized the planned maneuver.

The measure represents the biggest expansion of the social safety net since Medicare was enacted more than 50 years ago.

It provides health coverage to 32 million people now uninsured, bars insurance companies from denying coverage to those in poor health, and sets up new marketplaces where self-employed people and small businesses can pool together to buy coverage.

Republicans, unanimous in their opposition, complained anew about the bill. Senate GOP Leader Mitch McConnell of Kentucky said a fuller analysis of the bill's long-term costs is needed, but Democrats have left no time to carry it out.

House Democratic leaders said they were getting closer by the hour. "We are on the verge of making great history for the American people," said House Speaker Nancy Pelosi, D-Calif.

In a flashback to the day in 2007 when Obama announced his presidential bid in Springfield, Ill., the president repeatedly invoked Lincoln's perseverance in the face of divisions — "We are not bound to win, but we are bound to be true."

"I know this is a tough vote," the president said, adding he also believes "it will end up being the smart thing to do politically."