Stung by the costly savings and loan crisis, the Treasury Department and General Accounting Office are recommending far-reaching changes in the regulation of the Federal National Mortgage Association, the Federal Home Loan Mortgage Corp. and five other private corporations that have been created by the government to finance housing, agriculture and education.

The Treasury yesterday called on Congress to give a government agency the power to regulate the organizations, which commonly are known by such nicknames as Fannie Mae, Freddie Mac and Sallie Mae. The Treasury also said that the government-backed companies should be required to bolster their financial structures so they can qualify for the safest possible credit ratings without any government support.

Similar but less specific recommendations are made, according to well-informed sources, in a GAO analysis scheduled to be released in about a month of what are classified as "government-sponsored enterprises" or GSEs. The enterprises have issued $862 billion worth of securities that could require taxpayer support, but they are all but unregulated, the Treasury said.

Sallie Mae -- the Student Loan Marketing Agency, which finances college loans -- has no regulator at all. The two biggest enterprises -- the Federal National Mortgage Association, or Fannie Mae, and the Federal Home Loan Mortgage Association, or Freddie Mac -- are nominally regulated by the Department of Housing and Urban Development, but that agency does not have any employees assigned full time to oversee their $650 billion businesses.

The Treasury and GAO studies were ordered by Congress as part of last year's savings and loan cleanup legislation.

The two agencies were told to find out whether the enterprises potentially could require the same kind of costly rescue as the thrift industry and what could be done to minimize the risk to taxpayers.

Both the Treasury and GAO have concluded that none of the government-backed businesses is in any immediate danger of failure.

In a draft of its report, however, the GAO warned that "caution dictates that the government not wait for a crisis ... "

Although Congress has never promised to bail them out, neither the GAO nor Treasury disputes that the government would have to stand behind the enterprises because they have grown so big that their failure would threaten the nation's financial system.

Designed to provide lower cost loans to government-favored borrowers, the various enterprises all work in the same general way. They raise money in financial markets for loans to college students, home buyers and farmers.

Making changes in the way the enterprises work could mean slightly higher interest rates for home buyers and farmers, officials of the agencies say. Treasury officials say any increase would be only a small fraction of a percentage point and would be worth the cost because it would protect taxpayers in general from a future bailout.

Besides better regulation, the Treasury and GAO say the taxpayers should be protected by requiring the enterprises to have adequate capital to protect against possible losses.

Some congressional critics of the enterprises have said they should be required to meet the same capital standards as banks and thrifts, but the Treasury study, directed by Deputy Assistant Secretary Michael Basham, suggests a private-sector approach. It says the agencies should be required to qualify for AAA credit ratings, the top grade given by private credit evaluation companies such as Standard & Poor's or Moody's.

The Treasury study concludes that the riskiest of the enterprises is the Farm Credit System, which has already gotten into financial trouble.

The studies focus more closely on Fannie Mae and Freddie Mac, which are the District's biggest financial institutions and two of the biggest local employers with almost 5,000 people on their payrolls. The two are the nation's biggest providers of home mortgages.

Fannie Mae's businesses are riskier because it is bigger and invests more of its own money in mortgages, while Freddie Mac uses financing methods that reduce risks. The danger to both companies, government officials said, is that a severe downturn in the economy or a sharp, sustained run-up in interest rates could cause home buyers to default on their mortgages.

Fannie Mae Chairman David Maxwell and Freddie Mac Chairman Leland Brendsel both made clear they will oppose many of the Treasury recommendations in Congress and warned that excessive regulation could raise mortgage costs.

Asking Freddie Mac to qualify for a AAA credit rating "has a cost that will be borne by home buyers," said Brendsel, who said taxpayers could be protected by a slightly lower rating at a much lower cost. Said Maxwell: "I am a little skeptical of whether it is appropriate, given the public policy purposes of Fannie Mae, to give the determination of what we do to a rating agency that is not part of the government."

Fannie Mae recently announced plans to raise about $2.5 billion in additional capital in the next couple of years, but it is not clear whether that will be enough to qualify for the AAA credit rating.