An economic slowdown in China and other major developing countries has pulled one of the few remaining props from the world economy, which is already threatened by the financial crisis in Europe and a sluggish U.S. growth.

Strong growth among developing countries, particularly the so-called “BRIC” nations – Brazil, Russia, India and China – as well as Mexico and South Africa, had been a bright spot in an otherwise tepid world recovery.

No longer.

Growth is now slowing among those nations as well. And for a variety of reasons, they may not be able to respond with the same intensity as they did after the U.S. financial collapse in 2008, when they pumped hundreds of billions of dollars into government projects and other measures to stimulate their economies.

Those efforts kept their own economies on track and helped ease the recession in the developed world by boosting the demand for exports from countries such as the United States. Sales to China from the United States, for example, jumped more than 80 percent between the first months of 2009 and the first months of 2012.

That rapid run-up is losing steam, prompting the International Monetary Fund on Monday to trim its forecasts for global growth and warn that worse problems may be in the offing.

This could also spell a further drag on the U.S. economy, which is struggling with an 8.5 percent unemployment rate.

“World leaders are casting around for some source of growth outside their own borders, and it is increasingly hard to find,” said John G. Murphy, vice president for international affairs at the U.S. Chamber of Commerce. “The past two years have seen rapid export growth (in the United States). There is a growing concern that is behind us.”

The chief global worry remains Europe, where agency officials acknowledged that the emergency steps taken so far have failed to remove the financial pressures on the major economies of Italy and Spain and ensure that their governments will be able to continue raising money from investors. In some of their bluntest language yet, top IMF analysts said the European Central Bank may need to resume buying government bonds. Otherwise, Italy and Spain could be forced to seek massive international bailouts, which could paralyze world financial markets.

IMF officials also warned that the U.S. economy has its own threats. In particular, the United States is facing the danger later this year that political gridlock may prevent the government from raising its borrowing limit, which could lead to national default, and from heading off the enormous spending cuts due to take effect next year. The latter could could drive the United States back into recession.

The IMF’s warning about worsening conditions in the developing world was evidence that the global economic recovery remains vulnerable despite repeated rounds of government stimulus and years of low interest rates.

A slowdown in the developing world was not totally unexpected. Developing countries depend heavily on exports to the richer developed world, where economic conditions have remained difficult.