The United States economy has lost the momentum it appeared to be building earlier this year, as the latest government statistics showed that it expanded by a mere 1.5 percent annual rate in the second quarter.


The mired recovery makes the United States more vulnerable to trouble in Europe and, at home, the potential expiration of several tax breaks and other buoyant measures at the end of the year, known as the fiscal cliff. It also illustrates the election-season challenge to President Obama, who must sell his economic record to voters as the recovery slows.


Growth, as measured by the gross domestic product, lagged as consumers curbed new spending and businesses held back. Several bright spots in the first three months of the year, including auto production, computer sales and large purchases like appliances and televisions, dimmed or faded away altogether in the second quarter, and government at all levels continued to cut spending. Growth was not strong enough to drive down the unemployment rate, which has stalled above 8 percent in recent months.


The lackluster figure immediately gave Mr. Obama’s opponents the opportunity to question the federal government’s response to the financial crisis, though a vast majority of economists agree that the stimulus and the bank bailouts saved jobs. House Speaker John Boehner said the G.D.P. report, released Friday by the Commerce Department, showed “the need to stop all of the looming tax hikes.” The report also spurred calls from liberals for the government to do more.


The Federal Reserve, which has lowered its forecasts in recent weeks, is watching the slowdown carefully as it considers further stimulus, though several analysts said Friday that they doubted that new action from the Fed could have much effect.


“Given where interest rates are, I think it should be evident that we’re in one of those spots where in order to lift growth, government needs to spend money,” said Steve Blitz, the chief economist at ITG Investment Research.


The economy is following a pattern established over several years now — hopes raised by modest acceleration that later fizzles out — that underscores the notion that rebounds after financial busts take their own excruciating time.


This year, some of the weakening was to be expected after a spurt of activity during an unseasonably warm winter. A mild uptick is expected in the second half of the year, driven in part by lower gas prices.


But improvement strong enough to provide real traction or lower the jobless rate remains out of reach. While the economy has not entered a downward spiral in which weakness feeds on itself, wrote Jim O’Sullivan, the chief United States economist for High Frequency Economics, an analysis firm, “there does not appear to be much basis for expecting a significant pickup any time soon.”


The government also provided on Friday a revised figure for first-quarter G.D.P., saying the economy then grew by a 2 percent annual rate. The previous estimate was 1.9 percent.


A slowdown in household spending is still hampering economic growth. Consumers increased their savings rate, a sign of increased uncertainty about the future. Governments also continued to cut spending. Exports accelerated in the second quarter despite more recent signs of diminishing demand, but the gain was canceled out by a larger increase in imports, which count against the gross domestic product. Economists expect exports to shrink as the dollar rises against other currencies, making American goods less competitive.


The housing sector, which has gone from a drag on the economy to a positive, continued to grow, posting a 9.7 percent gain — though again, that is less than half its rate of growth in the first quarter.


Uncertainty cast a pall, coming from both the domestic front, with a presidential race and the fate of numerous federal policies in question, and from overseas, with companies like Ford reporting a decline in profit this week because of the slowdown in Europe, despite a healthy showing in North America.


“You can’t blame all of it on Europe — we have our own problems yet,” said Joshua Shapiro, the chief United States economist at MFR Inc., a financial consulting firm. “When you have a credit bubble or asset bubble that’s popped, the recovery process from that is just really long and really painful.”