WASHINGTON, US - The US Senate's Democratic majority was poised to unveil a 10-year, 849-billion-dollar (S$1177 billion) bill to overhaul US health care on Wednesday, with a key first test vote this weekend, a leadership aide said.

Democratic Senate Majority Leader Harry Reid called fellow Democrats together for a 5 pm (2200 GMT) meeting to discuss the bill, and is likely to hold a press conference later, the aide said on condition of anonymity.

Reid had been waiting for the non-partisan Congressional Budget Office (CBO) to send back a preliminary estimate of the cost of the legislation, which would enact President Barack Obama's top domestic priority.

The CBO estimates the measure will cost 849 billion dollars over 10 years, below Obama's self-imposed 900-billion-dollar ceiling, and will cut the budget deficit by 127 billion dollars over the same period, the aide said.

It will extend coverage to 94 percent of Americans, and reduce the rolls of uninsured Americans by 31 million people, the aide told reporters.

Reid is expected to seek a vote as early as Saturday on proceeding to the bill, which would be a key early test of support in the Senate, where he needs 60 votes to ensure passage of the legislation.

The House of Representatives narrowly adopted its version of the legislation on November 7, squeaking by on a 220-215 vote.