The US government yesterday seized control of mortgage finance companies Fannie Mae and Freddie Mac , launching what could be its biggest federal bailout ever, in a bid to support the US housing market and ward off more global financial market turbulence.

Officials were concerned that mounting losses at the two companies, which own or guarantee almost half of the country's $12 trillion in outstanding home mortgage debt, was sapping their vitality and threatening to undermine them at a time other sources of housing finance have largely run dry.

"Our economy and our markets will not recover until the bulk of this housing correction is behind us," US Treasury Secretary Henry Paulson said at a news conference. "Fannie Mae and Freddie Mac are critical to turning the corner on housing."

The two companies, publicly traded but also serving a government mission to support housing, were put in a conservatorship that allows their stock to keep trading but puts common shareholders last in any claims.

Their top executives were ousted. Freddie Mac chief executive Richard Syron and Fannie Mae's CEO, Daniel Mudd, were replaced by David Moffett, a former top official at US Bancorp and Herb Allison, formerly with Merrill Lynch and pension fund TIAA-CREF.

In addition, the U.S. Treasury will immediately take a $1 billion equity stake in each company in the form of senior preferred stock and if needed could inject up to $100 billion into each firm.

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