As America’s biggest banks prepare to announce tens of billions of dollars in fresh writedowns from the international credit squeeze, they are turning to unlikely rescuers.

Sovereign wealth funds – or state-backed investors – are expected to buy further stakes in Merrill Lynch and Citigroup as the banks try to repair their battered balance sheets. The funds’ role may be unnerving for some in Washington. But their involvement is as welcome as it will be necessary if the US economy is to avoid a prolonged slump.