Fannie Mae and Freddie Mac shares fell again Friday  and the broader stock market followed suit  as concern mounted that the government will be forced to take over the beleaguered mortgage finance companies, which some investors fear are at risk of default.

Even after a week of unprecedented losses, the companies’ declines early Friday were the sharpest yet: Freddie Mac shares were down more than 50 percent early in the day before paring their losses in the afternoon. Freddie Mac closed down 3.1 percent, at $7.75. Fannie Mae stock fell as much as 49 percent before rallying and ended down more than 22 percent, at $10.25.

Investors, meanwhile, snapped up debt issued by those companies, and the insurance premiums on those securities dropped sharply on the view that they would be protected by a government takeover.

Image Traders on the floor of the New York Mercantile Exchange. Oil prices spiked above $147 a barrel on Friday. Credit... Chang W. Lee/The New York Times

The Bush administration sought to allay market fears. The president, after meeting with his team of economic advisers Friday morning, said he was briefed on the situation by Treasury Secretary Henry M. Paulson Jr.