NEW YORK — Bear Stearns Cos. said Thursday a bigger-than-expected writedown in its mortgage portfolio caused the nation's fifth-largest U.S. investment bank to post the first loss in its 84-year history.

It took a $1.9 billion writedown in the quarter ended Nov. 30 as its mortgage-backed securities continued to lose value amid the global credit crisis. That was much larger than the $1.2 billion it expected in November.

Bear Stearns' fiscal fourth-quarter loss, and collapse of two hedge funds it managed during the summer, prompted Chief Executive Jimmy Cayne to pass on his 2007 bonus. Members of the company's executive committee also will not receive year-end bonuses.

Cayne is under pressure like other chief executives on Wall Street as global banks have written off more than $100 billion in assets this year. Bear Stearns and other firms have seen writedowns from subprime-related investments and fixed-income trading come in much steeper than first expected.