WASHINGTON — Health care legislation backed by President Barack Obama all but cleared a major hurdle in the Senate early this morning as Democratic liberals and moderates on a key committee closed ranks behind the most sweeping set of changes in a half-century.

The legislation is designed to spread health insurance to millions who now lack it, and cracks down on industry practices such as denying coverage on the basis of pre-existing medical conditions.

More than $400 billion in federal subsidies would help defray premium costs for lower-income families and help small businesses offer coverage to their workers. Most policies would be required to cover preventive care as well as treatment for medical illness and vision, dental and mental health needs.

It was past 2 a.m. when Sen. Max Baucus, D-Mont., the committee chairman, announced that work had been completed on all sections of the legislation.

"This bill will lower taxes for more than 42 million Americans and reduce the federal deficit," he said. "This bill will protect Medicare benefits for seniors. This bill will significantly expand health coverage."

A final vote was delayed until next week so budget officials can certify the legislation does not add to federal deficits. Given the Democrats' 13-10 majority, only the final margin is in doubt.