WASHINGTON — The Federal Reserve said Wednesday that the United States economy was slowing more than it had previously thought and painted a far less rosy economic picture than the White House as it left interest rates unchanged and signaled little appetite for raising them again in the near future.

Jerome H. Powell, the Fed chairman, said the economy “is in a good place” in a news conference. But he and his colleagues said growth appeared to be slowing from last year, under the weight of the Trump administration’s trade war, economic slowdowns in Europe and China and fading stimulus from the Republican tax cuts of 2017.

The Fed now expects 2.1 percent growth this year, down from the 2.3 percent it forecast in December — and more than a percentage point less than the 3.2 percent growth the White House predicts. The outlook for 2020 is even more bleak, with the Fed now projecting growth of just 1.9 percent.

The downbeat assessment comes as the Fed sees signs of weakness in areas like consumer spending and business investment, which Mr. Powell said “suggest that growth is slowing somewhat more than expected.” Average monthly job growth, while strong, “appears to have stepped down from last year’s strong pace,” he added.