WASHINGTON — Federal housing officials on Tuesday served subpoenas on 15 mortgage companies that have suspiciously high default rates for loans backed by the Federal Housing Administration.

The Department of Housing and Urban Development's Office of Inspector General said it wanted to determine why defaults are so elevated among those companies and whether any have committed fraud.

"Many of these target loans didn't last but a short time before defaulting," said Kenneth Donohue, the inspector general. "We will conduct an investigation, if appropriate, to determine who is responsible and will recommend that appropriate action be taken against individuals and corporations."

The Federal Housing Administration is a major source of funding for first-time homebuyers. The agency, which insures roughly 30 percent of new loans, has seen its losses rise with the unemployment rate. There also have been fears that subprime lenders have shifted their business to the FHA after the subprime business went bust.

The FHA does not make loans, but rather offers insurance against default. Borrowers are willing to pay for the insurance because FHA loans only require down payments of 3.5 percent of the purchase price.

The lenders targeted by FHA officials include some of its worst-performing active lenders. For example, almost one in five loans made by Alethes LLC of Lakeway, Texas, over the past two years went into default, compared with a national average of about 5 percent.

"We are reviewing each of these files to determine what commonalities there are, if any," said Danny Smith, president of Alethes, wrote in an e-mail.

Two other FHA lenders being targeted, Alacrity Lending Co. of Southlake, Texas and Pine State Mortgage Corp. of Atlanta, each had default rates of about 15 percent. A call to Alacrity was not immediately returned. Pine State Mortgage could not be immediately reached for comment and the company's Web site was down Tuesday afternoon.