US President Barack Obama has described a congressional vote on healthcare reform due on Sunday as a "historic" moment in a century-long struggle.
Speaking at a rally in Virginia, he dismissed criticism of the bill from Republicans and some Democrats.
Appealing to lawmakers and citizens to back the legislation, he said: "The time for reform is right now."
Democrats are still working to secure enough House of Representatives votes to pass a Senate version of the bill.
The BBC's Mark Mardell in Virginia says that Mr Obama's speech was fiery but the Democratic Party seems deflated, with no real desire to motivate the people.
The reforms would deliver on Mr Obama's top domestic priority by providing insurance to some 30 million Americans who currently lack it.
Calling the battle to create the bill, "messy", "frustrating" and "ugly", Mr Obama said the final proposal was the culmination of a year of "hard debate".
"Every argument has been made," he told students at George Mason University.
"We have incorporated the best ideas from Democrats and Republicans into a final proposal."
The House of Representatives and the Senate adopted different versions of the bill in November and December.
The usual procedure would be for two versions of legislation to be combined into a single bill for President Obama to sign into law. But after Senate Democrats lost the 60-seat majority required to defeat a filibuster by Republicans, Democratic leaders decided to use a controversial procedure to ensure the bill's passage.
Under the plan, the House will vote on a package of reconciliation "fixes" amending the Senate bill.
'Bill of rights'
The Senate will then be able to make changes in a separate bill using a procedure known as reconciliation, which allows budget provisions to be approved with 51 votes - rather than the 60 needed to overcome blocking tactics.
Mr Obama brushed aside Republican claims that the bill was too costly and said Americans had been told "a whole bunch of nonsense" about its contents.
The reform, he said, "brings our deficit down by more than one trillion dollars over the next two decades. Not only can we afford to do this. We can't afford not to do this."
According to Congressional Budget Office, the final version of the Democrats' healthcare plan will cut the federal deficit by $138bn over 10 years.
The non-partisan body said the proposed legislation would cost about $940bn over a decade.
The president also lashed out an insurance companies whose lobbyists, he said, were prowling the corridors of Washington, trying to prevent the bill passing.
"We are going to end the worst practices of insurance companies. This is a patients' bill of rights on steroids," he told a cheering crowd.
The reforms would increase insurance coverage through tax credits for the middle class and expansion of the Medicaid programme for the poor.
If approved, they would represent the biggest change in the US healthcare system since the creation in the 1960s of Medicare, the government-run scheme for Americans aged 65 or over.