The Congressional Budget Office said on Wednesday that an alternative health care bill put forward by House Republicans would have little impact in extending health benefits to the roughly 30 million uninsured Americans, but would reduce average insurance premium costs for people who have coverage.

The Republican bill, which has no chance of passage, would extend insurance coverage to about 3 million people by 2019, and would leave about 52 million people uninsured, the budget office said, meaning the proportion of non-elderly Americans with coverage would remain about the same as now, at roughly 83 percent.

The budget office has said that the Democrats’ health care proposal would extend coverage to 36 million people, meaning that 96 percent of legal residents would have health benefits. The Democrats’ bill would cost $1.1 trillion, with the costs more than covered by revenues from new taxes or cuts in government spending, particularly on Medicare.

House Republicans, including their leader, Representative John A. Boehner of Ohio, have said that they did not intend for their legislation to expand insurance coverage, because they viewed that goal as unaffordable. Instead, they said the bill was tailored narrowly to reduce costs.

According to the report by nonpartisan budget office, the Republican bill would reduce future federal deficits by $68 billion over 10 years, compared to a reduction of $104 billion by the House Democrats’ legislation.

The findings by the budget office mostly seemed to confirm assertions by Democrats that the Republican bill, offered as an amendment to the Democrats’ measure, would do little to change the status quo.

But Republicans will certainly find aspects of the cost analysis to brag about. The budget office predicted savings for the federal government of $41 billion over 10 years as a result of provisions to limit costs related to medical malpractice lawsuits.

In addition, many Republicans have said the country cannot afford a hugely expensive health care bill at a time of staggering federal deficits, and the total cost of insurance provisions in the Republican bill would be just $61 billion compared to $1.1 trillion for the Democrats’ bill.

The budget office also said that the Republican bill would reduce average insurance premiums, though the budget office cautioned that its calculations in that regard were subject to a high degree of uncertainty.

The budget office said that in the Republican plan, premiums would be reduced the most for people who buy insurance in the individual or small-group market, but that people who get large-group insurance through their employers would also see some reduction in cost. “The combination of provisions included in the amendment would reduce average private health insurance premiums per enrollee in the United States relative to what they would be under current law,” the budget office said.

It said premiums would be cut by 7 percent to 10 percent in the small group market; by 5 percent to 8 percent in the individual market; and by up to 3 percent in the large group market, which is where 80 percent of Americans get their coverage.

The budget office carefully hedged its findings, writing: “Some provisions of the legislation would tend to decrease the premiums paid by all insurance enrollees, while other provisions would tend to increase the premiums paid by less healthy enrollees or would tend to increase the premiums paid by enrollees in some states relative to enrollees in other states. As a result, some individuals and families within each market would see reductions in premiums that would be larger or smaller than the estimated average reductions, and some people would see increases.  The estimates of changes in average premiums are very preliminary and are subject to an unusually high degree of uncertainty.”

Republicans hailed the budget office findings as evidence that they had produced a superior bill, while Democrats ridiculed the same findings as evidence that the Republican bill would accomplish virtually nothing.

“Across the country the American people are calling on Washington to pass responsible reform that will lower health care costs,” Representative Mike Pence of Indiana, the No. 3 House Republican said in a statement late Wednesday. “Yesterday, House Republicans answered that call by putting forward common-sense health care legislation that reduces the deficit, lowers premiums, and ensures coverage for those with pre-existing conditions.”

But Representative George Miller, Democrat of California, chairman of the Education and Labor Committee and one of the main architects of the Democrats’ bill, said the Republicans had come up short.

“Tonight CBO confirmed that the Republicans’ only solution for health reform is to preserve the status quo,” Mr. Miller said in a statement. “It will leave 52 million Americans literally out in the cold, does nothing to help low-income and middle-class families afford quality health care, and protects insurance companies’ power to deny claims and stand between patients and their doctors.”