Washington ? President Barack Obama’s health care overhaul law will increase the nation’s health care tab instead of bringing costs down, government economic forecasters concluded Thursday in a sobering assessment of the sweeping legislation.

A report by economic experts at the Health and Human Services Department said the health care remake will achieve Obama’s aim of expanding health insurance — adding 34 million Americans to the coverage rolls.

But the analysis also found that the law falls short of the president’s twin goal of controlling runaway costs, raising projected spending by about 1 percent over 10 years. That increase could get bigger, however, since the report also warned that Medicare cuts in the law may be unrealistic and unsustainable, forcing lawmakers to roll them back.

The mixed verdict for Obama’s signature issue is the first comprehensive look by neutral experts.

In particular, the warnings about Medicare could become a major political liability for Democratic lawmakers in the midterm elections. The report projected that Medicare cuts could drive about 15 percent of hospitals and other institutional providers into the red, “possibly jeopardizing access” to care for seniors.

The report from Medicare’s Office of the Actuary carried a disclaimer saying it does not represent the official position of the Obama administration. White House officials have complained that such analyses have been too pessimistic and lowball the law’s potential to achieve savings.

The report acknowledged that some of the cost-control measures in the bill — Medicare cuts, a tax on high-cost insurance and a commission to seek ongoing Medicare savings — could help reduce the rate of cost increases beyond 2020. But it held out little hope for progress in the first decade.

“During 2010-2019, however, these effects would be outweighed by the increased costs associated with the expansions of health insurance coverage,” wrote Richard S. Foster, Medicare’s chief actuary. “Also, the longer-term viability of the Medicare … reductions is doubtful.” Foster’s office is responsible for long-range costs estimates.

Republicans said the findings validate their concerns about Obama’s 10-year, nearly $1 trillion plan to remake the nation’s health care system.

“A trillion dollars gets spent, and it’s no surprise — health care costs are going to go up,” said Rep. Dave Camp, R-Mich., a leading Republican on health care issues. Camp added that he’s concerned the Medicare cuts will undermine care for seniors.