July 16 (Bloomberg) -- IndyMac Bancorp Inc., the California mortgage lender seized by regulators last week, is under investigation by the FBI, people familiar with the probe said.

The Federal Bureau of Investigation's Los Angeles office is leading the review, which one federal official said was preliminary. The agents are working closely with the Federal Deposit Insurance Corp. The FDIC re-opened the company this week as IndyMac Federal Bank FSB after the seizure.

Authorities are looking at whether the bank committed fraud in connection with loans made to home buyers with poor credit, the people said.

The Pasadena, California-based lender specialized in so- called Alt-A mortgages, which didn't require borrowers to document their incomes. The bank is the second-biggest federally insured financial institution taken over by the government.

The FBI, responding to the subprime loan crisis that has rocked Wall Street and led to the worst housing slump since the Great Depression, has 21 corporate fraud probes of investment banks, hedge funds and mortgage companies. It also has more than 1,400 pending mortgage fraud cases looking at individuals such as brokers, appraisers and borrowers.

People familiar with the probe have said that among the other companies under FBI scrutiny is Countrywide Financial Corp., the largest U.S. mortgage lender. Countrywide was taken over by Bank of America Corp. on July 1.

Last month, two former Bear Stearns Cos. investment managers, whose hedge funds' collapse helped ignite the subprime meltdown, were indicted by a federal grand jury in Brooklyn, New York. Both men have said they will fight the charges.

Richard Kolko, an FBI spokesman, and FDIC spokesman Andrew Gray declined to comment on IndyMac.

To contact the reporter on this story: Robert Schmidt in Washington at rschmidt5@bloomberg.net.

Last Updated: July 16, 2008 18:12 EDT