The IMF blames the lingering aftermath of the brutal winters and a sluggish recovery in home sales. Years of disappointing growth mean the economy might not reach full employment — which many economists say is when the unemployment rate is between 5 and 5.5 percent — for three more years.
Christine Lagarde, the IMF's managing director, suggested at a news conference that the past winter shows that another wild card might be holding back the economy and could make predictions more difficult: climate change.
"Extreme weather occurrences have repeated much more frequently in the past 20 years than the previous century," she stressed. "That's a reason to wonder about climate change and how to deal with it."
Yet the IMF is optimistic that a "renewed dynamism" will propel growth for the rest of 2014, partly offsetting what many analysts think was a contraction of up to 2 percent last quarter.
The unemployment rate has tumbled to 6.3 percent from 7.5 percent in 12 months, evidence of that momentum.
But the IMF cautions that U.S. wages remain stagnant and the rate of long-term unemployment high. As a result, it urged lawmakers to lift the minimum wage and increase the Earned Income Tax Credit for those with low wages.
The IMF projects that growth will reach 3 percent in 2015, roughly matching the United States' average rate of expansion between 1948 and 2007. But even the 2015 estimate was a downward revision from the IMF's previous forecast that growth next year would be 3.5 percent.
The IMF's projections for 2014 match many recent private forecasts.
"The monthly economic numbers have generally been pretty good recently, but the weakness of GDP growth in the first quarter suggest that full-year GDP growth is likely to be close to 2 percent," said Ryan Wang, an economist at HSBC Bank.
The IMF also highlighted the challenge for the Federal Reserve to properly time the unwinding of its policies to spur borrowing, investment and spending. Investors appear to be acting with a sense of certainty about Fed policies, even though central banks must respond to uncertainties about the economy, Lagarde said.
Lagarde also suggested that Fed Chair Janet Yellen should increase the number of news conferences she holds to up to six a year from the current four. Yellen is scheduled to hold one of her quarterly news conferences on Wednesday.
The Fed has kept short-term interest rates near zero to bolster the economy. It has also bought U.S. Treasury and mortgage bonds to keep longer-term rates low, a program the Fed has been unwinding since the start of the year.
Because the IMF projects that the United States won't reach full employment until 2017 and that inflation pressures will stay tame, it thinks the Fed might consider keeping rates near historic lows longer than some market analysts expect.
Raising rates too fast could "constrict the recovery momentum that we have observed," Lagarde said. She added that that would have spillover effects around the world and hurt growth in emerging economies.