“If you go out and talk to doctors and hospital executives, they believe their world is changing,” said Peter Orszag, a former budget director in the Obama administration and now a vice chairman at Citigroup. “Nothing in life is conclusive, but I think the case for this being at least partially structural is much stronger than the case for it being entirely cyclical.”

The slowdown has occurred in both government and overall health spending. From 2009 to 2011, total health spending grew at the lowest annual pace since the government started keeping records 52 years ago, a trend that seems to have continued last year. In the 2012 fiscal year, Medicare spending per beneficiary grew just 0.4 percent. The new Congressional Budget Office data said that overall Medicare outlays grew 3 percent in 2012, the slowest rate since 2000.

A major question raised by Mr. Elmendorf and others is whether the spending will accelerate again. (It slowed in the 1990s only to pick up again last decade.) “There’s a lot of reasons to suspect it’s temporary,” said Douglas Holtz-Eakin, a former director of the Congressional Budget Office and a prominent Republican economist. “Premature celebration never makes sense when it comes to health care,” he added.

Slower cost growth would have ramifications far beyond the deficit. According to calculations by White House economists, slowing the annual growth rate of health care costs by 1.5 percentage points might increase economic output by 2 percent in 2020 and 8 percent in 2030. It might also lead to higher wages for workers and more room for productive investments in the budget.

Even if the slowdown continued, the deficit problem would hardly be solved, budget experts said. One situation described by the Altarum Institute imagines tax revenue at about 19 percent of economic output and health care spending growing about as fast as economic output did. Assuming a balanced budget, that would leave 6 percent of economic output for spending on defense, safety net programs and other nonhealth programs in 2035. The modern low is around 8 percent, Mr. Roehrig said.

“It is possible to keep the policies for those large benefit programs unchanged, but only by raising taxes substantially for a broad segment of population,” Mr. Elmendorf said. “Alternatively, it’s possible to keep tax revenues at their historical average of percentage of G.D.P., but only by making substantial cuts relative to current policies in the large benefit programs that aid a broad group of people at some point in their lives.”