IndyMac Bank, a prolific mortgage specialist that helped fuel the housing boom, was seized Friday by federal regulators, in the third-largest bank failure in U.S. history.

IndyMac is the biggest mortgage lender to go under since a fall in housing prices and surge in defaults began rippling through the economy last year -- and it likely won't be the last. Banking regulators are bracing for a slew of failures over the next year as analysts say housing prices have yet to bottom out.

The...