Congressional budget crunchers said Thursday that the Democrats’ latest health-care plan would hold down federal red ink for at least 20 years, an assessment that gave supporters hope as the Senate moved toward a historic debate.

The nonpartisan Congressional Budget Office said that Senate Majority Leader Harry Reid’s 10-year, $848 billion bill would produce a net reduction of $130 billion in federal deficits in its first decade.

Perhaps more significantly, the legislation would continue to give back over the next 10 years and beyond, the budget office said, because “added revenues and cost savings would probably be greater” than the cost of covering uninsured Americans.

The budget office put an asterisk on its forecast, using words such as “imprecision ...