The large number of Americans who currently have employer-sponsored medical insurance would not see much change in their premium costs as a result of the health care legislation pending in Congress, according to a widely awaited budget analysis.

The analysis, released Monday by the nonpartisan Congressional Budget Office estimates the impact on health insurance premiums under the sweeping legislation being championed by the Obama administration and Democratic leaders on Capitol Hill.

The analysis found that premiums would move in many different directions for different types of people in different circumstances. But in perhaps the most crucial finding, the budget office said that the large number of Americans who currently have employer-sponsored insurance would see little change in their premium costs — and that in some cases the costs might even fall.

Employment-sponsored coverage would account for about five-sixths of the total health insurance market, the budget office said.

Because calculating the proposed legislation’s effect on premiums is so complicated, the budget office pegged its analysis to a single year, 2016, and it focused on the average premium “per person – that is, per covered life, including dependents covered by family policies.”

For the small group market — that is, employers with 50 or fewer employees — the change in premium prices for those policies would range from an increase of 1 percent to a reduction of 2 percent in 2016, as compared to projections of premium prices under current law, the budget office said.

And for the large group market, defined as employers with more than 50 workers, “the legislation would yield an average premium per person that is zero to 3 percent lower in 2016,” the budget office reported.

Frustrating as it might seem, the analysis of premium pricing is complex, and the potential effect of the legislation varies greatly, depending on the individual circumstances of American individuals and families. And so, both sides in the political debate could find fodder for their arguments in support or in opposition to the legislation.

Senator Evan Bayh, Democrat of Indiana, who requested the budget office analysis, has warned that his support for the legislation would hinge on its not increasing insurance costs for Americans who already have coverage through their employers.

Some other Democrats hailed the analysis as supporting the value of the proposed legislation.

“In recent years, Americans have seen their health insurance premiums creep higher and higher at an alarming rate,” Senator Max Baucus, Democrat of Montana, and chairman of the Senate Finance Committee, said in a statement. “Health reform set out to slow those rapid increases, and today the non-partisan congressional budget scorekeepers told us we’ve succeeded.”

Mr. Baucus added: “The analysis we received today indicates that whether you work for a small business, a large company or you work for yourself, the vast majority of Americans will see lower premiums than they would if we don’t pass health reform.”

But there are wrinkles. The budget office found that the cost of insurance premiums for non-group policies – insurance bought directly by individuals – would increase 10 percent to 13 percent. But half of the people in the non-group market would receive federal subsidies that would drive the cost of insurance substantially lower than it would be under existing law.

In all, the non-group market is expected to account for about 17 percent of the total health insurance market.

One reason for the increase in prices in the non-group market is that policies would have to “cover a broader scope of benefits than are projected to be covered by such policies, on average, under current law,” the budget office said.

In other words, people who would end up paying more for their insurance would also be getting better coverage.

Still the possibility that costs could increase for anyone is likely to become fodder for opponents of the Democrats’ health care legislation.

The Senate Republican leader, Mitch McConnell of Kentucky, immediately seized on the budget office analysis to assert that the legislation was flawed and would increase costs.

“At the beginning of the health care debate, we were told that this trillion-dollar experiment would lower premiums for American families,” Mr. McConnell said in remarks prepared for a floor speech. “And yet just this morning, the independent Congressional Budget Office provided an analysis showing that the Democrat bill will actually increase premiums for American families. So a bill that’s being sold as a way to reduce costs actually drives them up.”

More coverage and analysis of the Congressional Budget Office report is expected in The New York Times and on nytimes.com