WASHINGTON  The Federal Bureau of Investigation is struggling to find enough agents and resources to investigate criminal wrongdoing tied to the country’s economic crisis, according to current and former bureau officials.

The bureau slashed its criminal investigative work force to expand its national security role after the Sept. 11 attacks, shifting more than 1,800 agents, or nearly one-third of all agents in criminal programs, to terrorism and intelligence duties. Current and former officials say the cutbacks have left the bureau seriously exposed in investigating areas like white-collar crime, which has taken on urgent importance in recent weeks because of the nation’s economic woes.

The pressure on the F.B.I. has recently increased with the disclosure of criminal investigations into some of the largest players in the financial collapse, including Fannie Mae and Freddie Mac. The F.B.I. is planning to double the number of agents working financial crimes by reassigning several hundred agents amid a mood of national alarm. But some people inside and out of the Justice Department wonder where the agents will come from and whether they will be enough.

So depleted are the ranks of the F.B.I.’s white-collar investigators that executives in the private sector say they have had difficulty attracting the bureau’s attention in cases involving possible frauds of millions of dollars.