NEW YORK — JPMorgan Chase & Co. Inc. came to the rescue of Washington Mutual Inc. Thursday, buying the thrift's banking assets after WaMu was seized by the Federal Deposit Insurance Corp. in the largest failure ever of a U.S. bank. This is the second time in six months that JPMorgan Chase has taken over a major financial institution crippled by bad bets in the mortgage market.

The deal will cost JPMorgan Chase $1.9 billion, and the bank said in a statement it planned to write down WaMu's loan portfolio by approximately $31 billion. JPMorgan Chase, which acquired Bear Stearns Cos. last March, also said it would sell $8 billion in common stock to raise its capital position.

The FDIC, which insures bank deposits, said it would not have to dip into the insurance fund as a result of the seizure. There had been concerns that the fund, which took a big hit after the seizure of IndyMac Bank, could be depleted by a WaMu seizure.

WaMu "was under severe liquidity pressure," FDIC Chairman Sheila Bair told reporters in a conference call.

"For all depositors and other customers of Washington Mutual Bank, this is simply a combination of two banks," Bair said in a statement. "For bank customers, it will be a seamless transition. There will be no interruption in services, and bank customers should expect business as usual come Friday morning."

The government measures bank failures by an institutions's assets; Seattle-based WaMu has roughly $310 billion in assets. The previous record was the failure of Continental Illinois National Bank in 1984, with $40 billion in assets when it closed. IndyMac, seized in July, had $32 billion.

WaMu was searching for a lifeline after piling up billions of dollars in losses due to failed mortgages; it has seen its stock price plummet 95 percent from a 52-week high of $36.47 to its close of $1.69 Thursday. On Wednesday, it suffered a ratings downgrade by Standard & Poor's that put it in danger of collapse.

The Bush administration's proposal for a $700 billion bailout for distressed financial institutions was believed to have given fresh impetus to a buyout and new allure to WaMu. However, it was not immediately known how a bailout, which was still being negotiated in Washington late Thursday, would affect the JPMorgan Chase-WaMu deal.

JPMorgan Chase's chief executive, Jamie Dimon, said in a conference call the "only negative" related to the deal was "how to handle some of these bad assets." He did not elaborate.

Besides JPMorgan Chase, Wells Fargo & Co., Citigroup Inc., HSBC, Spain's Banco Santander and Toronto-Dominion Bank of Canada were all mentioned as possible suitors. WaMu was also believed to be talking to private equity firms.

The FDIC was seeking a buyer will to bear a large burden of WaMu's losses to lessen the impact on the insurance fund.

In a statement, JPMorgan Chase said it was not acquiring any senior unsecured debt, subordinated debt, and preferred stock of Washington Mutual's banks, or any assets or liabilities of the holding company, Washington Mutual Inc.

JPMorgan Chase said the acquisition will give it 5,400 branches in 23 states. JPMorgan Chase said it plans to close less than 10 percent of the two companies' branches; the bank has not yet decided which to close.