US taxpayers could be on the hook for as much as $24 billion to rescue embattled Washington Mutual, the country's No. 1 savings and loan, a top banking analyst is warning.

The jaw-dropping tab would come in the form of federal mortgage loss guarantees needed to coax a buyer into purchasing WaMu, according to Landeburg Thalmann's Dick Bove, whose view on the need for a federal backstop is shared by an official with the Office of Thrift Supervision, WaMu's regulator.