UPDATE 1-FBI mortgage probe expands to 21 firms from 19

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WASHINGTON, July 16 (Reuters) - The FBI's investigation into potential corporate fraud in the U.S. home mortgage industry now encompasses 21 companies, up from 19 reported in April, a bureau spokesman said on Wednesday.

"It's up to 21 now," FBI spokesman Jason Pack said. He had no further details on the expansion. Bureau officials have regularly said they expect the number of corporate and individual mortgage fraud cases to grow amid a crisis in the U.S. home-lending industry.

The bureau has publicly acknowledged only one company -- Doral Financial Corp, as involved. The largest U.S. mortgage lender, Countrywide CFC.N, also is under FBI investigation, authorities have said, although the FBI has declined to comment and Countrywide said it was unaware of any investigation.

When the FBI disclosed its industry investigation, major investment banks Goldman Sachs (GS.N), Morgan Stanley (MS.N) and Bear Stearns Cos BSC.N each said the government had asked them for information, but there was no confirmation of any FBI role. Beazer Homes (BZH.N) said last year it had received a federal grand jury subpoena related to its mortgage business.

Pack also said he was unaware of any new FBI initiative to investigate potential stock manipulation in major financial firms, including housing finance giants Fannie Mae (FNM.N) and Freddie Mac (FRE.N) .

U.S. securities regulators issued an emergency rule on Tuesday to limit certain types of short selling in such firms.

(Reporting by Randall Mikkelsen)