The big question now is whether the federal government's move to take over Fannie and Freddie will restore investor confidence in the nation's credit markets, help stabilize the stock market and keep loans flowing to creditworthy borrowers.

Fannie and Freddie, by buying mortgages, provide banks and other financial institutions with fresh money to make new loans, a vital lubricant for the housing and credit markets.

As a result of the government's intervention, the cost of borrowing for Fannie Mae and Freddie Mac should decline, because the government will be insuring their debts. Equally important, because the government is backing the companies, they will continue to buy and sell home loans.

But the plan will probably do little to stop home prices from falling further. And foreclosures are almost certain to rise.

Just a week ago, Treasury officials were still considering a wide variety of options for Fannie Mae and Freddie Mac, ranging from doing nothing to taking over the companies completely, according to people with knowledge of those discussions.

The Treasury secretary, Henry M. Paulson Jr., who won authority from Congress last month to use taxpayer money to bolster the companies, always maintained that he hoped never to use that power. But, as the companies' stocks continued to languish and their borrowing costs rose, some within the Treasury Department began urging Paulson to intervene quickly.

Then, last week, advisers from Morgan Stanley hired by the Treasury Department to scrutinize the companies came to a troubling conclusion: Freddie Mac's capital position was worse than initially imagined, according to people briefed on those findings. The company had made decisions that, while not necessarily in violation of accounting rules, had the effect of overstating the company's capital resources and financial stability.

Indeed, one person briefed on the company's finances said Freddie Mac had made accounting decisions that pushed losses into the future and postponed a capital shortfall until the fourth quarter of this year, which would not need to be disclosed until early 2009. Fannie Mae has used similar methods, but to a lesser degree, according to other people who have been briefed.

Representatives of both companies did not return calls or declined to comment.

On Friday, executives from Fannie Mae and Freddie Mac were ordered to appear in the offices of their regulator, James B. Lockhart, in separate meetings, and were told that regulators were exercising their authority to place the companies in conservatorship, which would allow for uninterrupted operation of the companies but would put them under Lockhart's control.