WASHINGTON—The International Monetary Fund said the global economy is set to rebound sharply this year, with 3.9% growth, but the U.S. and other rich countries aren't likely to grow fast enough to reduce unemployment substantially.

Growth in what the IMF categorizes as "advanced countries" is expected to average only 2.1% this year and 2.4% in 2011, adjusted for inflation. "This growth will barely be enough to reduce the output gap and unemployment will remain high," said chief IMF economist Olivier Blanchard.

The...