Mr de Rato, Spain's former finance minister, was appointed to his post in 2004.

His replacement will come from Europe, as traditionally the continent provides the IMF leader, while the US provides the top person at the World Bank.

Mr de Rato has predicted that global growth for 2007 would be close to 5%.

"I have taken this decision for personal reasons. My family circumstances and responsibilities, particularly with regard to the education of my children, are the reason for relinquishing earlier than expected my responsibilities at the Fund," Mr de Rato said.

Institutions under strain

Under Mr de Rato, the IMF has taken an increasing role in what it calls "surveillance" of currencies, and has been a strong advocate of China revalunig its currency.

But it has struggled to find a role in managing global financial crises, as many Asian countries have built up large currency reserves following the Asian crisis ten years ago.

And it has begun a reform designed to give more power to fast-growing developing countries like China and India.

Meanwhile, the leadership of its sister institution, the World Bank, has also been in turmoil, with its boss, Paul Wolfowitz, forced to step down after allegations of favourtism.

The selection of his successor, former US trade representative Robert Zoellick, has raised questions about whether the process should be changed to make it more democratic and open.

Such calls - especially by developing countries - are likely to be renewed by Mr de Rato's resignation.