Over the weekend, the government announced plans to take over both Fannie Mae and Freddie Mac.

As part of the plan, the chief executives of both companies were replaced. Herbert M. Allison Jr., the former chairman of TIAA-CREF, the huge pension fund for teachers that also offers mutual funds, will take over Fannie Mae and succeed Daniel H. Mudd. At Freddie Mac, David M. Moffett, currently a senior adviser at the Carlyle Group private equity firm, succeeds Richard F. Syron. Mr. Mudd and Mr. Syron, however, will stay on during a transition period.

The plan also commits the government to provide as much as $100 billion to each company to backstop any shortfalls in capital. It enables the Treasury to ultimately buy the companies outright at little cost. It bans them from lobbying the government, putting an end to their ability to use their political machine on Capitol Hill.

It also eliminates dividend payments to current shareholders while protecting the principal and interest payments on the debt, now held by foreign central banks, financial institutions, pensions funds and others.

The Treasury will force both companies to shrink their portfolios over the long term; they now hold or guarantee about half of the country's mortgages. In addition, the government plans to buy significant amounts of their mortgage-backed securities on the open market, beginning with the purchase of $5 billion worth this month. This step, never before undertaken by the government, could begin to restore some confidence in the credit markets and lead to lower interest rates for home mortgages.

The stock market responded this morning by soaring over 300 points.