The US Congressional Budget Office says 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, which the House is expected to vote on at the weekend, would cost about $940bn over a decade.

President Barack Obama said the bill represented the most significant effort to reduce the deficit since the 1990s.

He has delayed a trip to Asia until June to help lobby wavering Democrats.

The reforms would deliver on Mr Obama's top domestic priority by providing insurance to some 30 million Americans who currently lack it.

They would increase insurance coverage through tax credits for the middle class and expanding 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.

Budget reconciliation

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.

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Under the plan, the House will vote on a package of reconciliation "fixes" amending the Senate bill.

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.

In a letter to House Speaker Nancy Pelosi, the Congressional Budget Office said a revised Senate bill would provide coverage to 32 million uninsured people by 2016, bringing the total number of insured to 95% of eligible Americans.

The measures would continue to reduce the federal deficit in its second decade, although such projections were uncertain, it added. Democrats say the total savings over 20 years will be $1.2 trillion.

Mr Obama said the bill represented "the most significant effort to reduce deficits since the Balanced Budget Act in the 1990s", when President Bill Clinton put the federal budget on a path to surplus.

"This is but one virtue of a reform that will bring the accountability to the insurance industry and greater economic security to all Americans," he added.

"I urge every member of Congress to consider this as they prepare for their important vote this weekend."

Later, White House spokesman Robert Gibbs announced that the president was postponing his trip to Indonesia and Australia until June so he could help Democrats rally last-minute support.

"The president believes right now the place for him to be is in Washington seeing this through," he said, adding that Mr Obama would apologise to President Susilo Bambang Yudhoyono and Prime Minister Kevin Rudd.

He had already delayed his departure until Sunday, the earliest possible date for a vote.

House Democratic leaders published the updated legislation on Thursday afternoon. They have promised that lawmakers will be given 72 hours to review it before voting.

Democratic leaders say they have not yet mustered the 216 votes they need for passage, but they are pressing ahead in the belief that they can get them.

Republicans are opposed to the proposed reforms, arguing they will give the government too much control over healthcare and be mainly paid for by higher taxes and cuts in Medicare.

House Republican leader John Boehner said they would "do everything that we can do to make sure this bill, never, ever, ever passes".