In his first full day on the job, Washington Mutual Inc. Chief Executive Alan Fishman pledged to return the Seattle savings-and-loan to profitability even as investors grew more doubtful about its prospects.

"I need to sit down and do a real dive into this thing," said Mr. Fishman, who was hired to succeed Kerry Killinger after WaMu's board concluded that an outsider was needed to help restore confidence.

Underscoring the magnitude of problems facing the Brooklyn-born Mr. Fishman is a memorandum of understanding with the Office of Thrift Supervision that was approved by WaMu's board in a Sunday board meeting.

The confidential document forces WaMu to provide the federal agency with what the company called "an updated, multi-year business plan and forecast for its earnings, asset quality, capital and business segment performance." WaMu said it isn't being required to raise additional capital or change any products or services.

Mr. Fishman promised to build "a winning model for the future" based on WaMu's 2,300- branch franchise, but he offered few details on how he would limit the company's credit exposure. He played down the need for additional capital and told analysts that it was too early to comment about possible asset sales. If the U.S. returns to a "more normalized credit environment," he said, the bank could free up an additional $4 billion to $6 billion a year.