The economy closed out a rough 2011 with the strongest growth in one and half years — but Uncle Sam doesn’t get a clean bill of health just yet.

The nation’s gross domestic product expanded at an annual rate of 2.8 percent in the fourth quarter, up from a feeble 1.8 percent in the third quarter but below economists’ forecast for 3 percent.

While the growth in the latest quarter was a sharp acceleration, experts don’t believe the economy will be able to keep up that pace of growth in 2012 — if not longer.

“The year overall was the slowest non-recessionary year of GDP growth since 1947 — hardly cause for a victory lap,” said Neal Soss, director of US economics at Credit Suisse.

“The economy shows symptoms of a slowdown. The fact that the economy has not managed a single quarter above 3 percent since the early stage of the recovery is telling in itself.”