Federal lawmakers are attempting to size up the risks posed by the secondary mortgage market in an effort to avoid saddling taxpayers with any future financial cleanup.

By most accounts, the two major secondary market players that provide lenders with funds to make home loans are in good financial shape. Nevertheless, Congress and the Bush administration want the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corp. (Freddie Mac) to further insulate taxpayers from bearing any losses should their fortunes ever sour.

The latest proposal on the table, however, has met with resistance from some lending community members who fear that it could drive up mortgage interest rates, dry up low-down-payment home loans and choke off the supply of condominium and vacation home loans.

The two financial intermediaries were created by Congress to attract funds needed to finance moderately priced residential real estate, currently with loans of up to $187,450. They package some of the loans they buy to sell to investors and use the money to buy more loans from primary lenders, while holding other loans themselves as investments. Over the years, the two companies have funded one out of every four mortgages that are now outstanding. The demand for their services has risen recently, with the two firms now backing two-thirds of new mortgage originations.

The two "government-sponsored enterprises," as they are known in government parlance, do not receive any federal funds. Yet the two firms' quasi-governmental status allows them to borrow funds on the capital markets at reduced rates that have lowered the cost of mortgage money to consumers by a half percentage point or more. The rate break stems from what the financial world has decided is an implicit guarantee that the federal government would cover any losses in the event either company goes under.

That implicit guarantee makes the taxpayers potentially liable for around $630 billion worth of obligations, not an insignificant figure given that the savings and loan industry cleanup is now expected to cost $300 billion over 10 years.

Rep. J.J. Pickle (D-Tex.) is among those in Congress worried that some day the federal government could end up footing the bill.

"Federal contingent guarantees, explicit or implicit, have a habit of becoming very real very quickly," Pickle recently told a conference on government-sponsored enterprises.

To lessen the likelihood the taxpayers would have to absorb any losses, Congress is taking a hard look at whether the two ventures have set aside sufficient capital, meaning the amount of company and shareholder money held in reserve.

The unique nature of the two firms, however, has prevented lawmakers from simply extending the same risk-based capital standards imposed on thrifts and commercial banks.

The Treasury Department recently recommended turning to the private credit-rating agencies to provide the necessary benchmarks. The rating companies grade the probability of a corporation losing money based on the riskiness of the debt it carries. Triple-A ratings go to the least risky ventures.

The Treasury would like to see Fannie Mae and Freddie Mac obtain triple-A ratings based solely on their own financial strength, as if no implicit federal guarantee existed. Should the companies fail to win those ratings within five years from at least two rating companies, then the federal government would sever all ties with the two companies, according to the Treasury Department recommendation.

In his testimony recommending the triple-A test, Treasury Undersecretary Robert R. Glauber called it the "superior method" for evaluating the capital adequacy of government-sponsored enterprises like Fannie Mae and Freddie Mac.

Thomas Gillis, a managing director at Standard & Poor's Corp., said his rating firm "preliminarily" considers Fannie Mae and Freddie Mac "investment grade" risks, which would put them in the triple-A to triple-B range. But, he said, they would not fall at the triple-A end of that spectrum. He said he could not offer a more concrete assessment because his firm has not studied the two companies in detail.

Fannie Mae currently has $3.7 billion worth of capital and has pledged to add another $2 billion to $2.5 billion by the end of 1991, according to David Jeffers, the firm's vice president for corporate relations.

Freddie Mac has $2.4 billion in capital under one set of accounting standards and $5.5 billion when measured in a different fashion, said Paul R. Allen, Freddie Mac's head of shareholder relations.

Few "independent financial entities" have achieved triple-A ratings, said Morgan Stanley & Co. stock analyst Nancy Spady, who objects to the Treasury's proposal. "It is not clear that any company in a single, undiversified line of business {such as residential mortgages} could qualify for this category," she said.

To raise their ratings, the firms could do a number of things, including increasing their fees to lenders, which would likely show up as higher interest rates, or shrinking their loan portfolios by making their loan products less attractive to the home-buying public.

Either of those strategies, warn critics of the triple-A rating proposal, could jeopardize the housing mission embraced by the two companies. One of the first casualties could be the half-percentage point interest rate break that consumers now enjoy, Spady said.

"If you make someone carry more capital than the economics of their business would normally dictate, then you are going to create unintended consequences," she said.

The triple-A rating system could also undermine the availability of mortgages with down payments of 10 percent or less, said Sam Lyons, a senior vice president at Great Western Bank, one of the largest U.S. lenders. The rating agencies, he predicted, will raise their estimates of risk for every small-down payment loan funded by the firms, which in turn would force them to put up more capital. That, said Freddie Mac's Allen, is what could happen if you rely on a "principally private-market rating that does not take into account our public policy purpose."

A contraction in the supply of mortgage money available through Fannie Mae and Freddie Mac would force lenders to use private mortgage conduits with unfavorable results, said Sidney Lenz, executive vice president of Countrywide Funding Corp., a nationwide lender based in Pasadena, Calif. "Wall Street wants to avoid certain things, like low down payments and some parts of the country, ... as well as certain types of properties, such as condos and second homes," she said.

A more meaningful way to determine whether Fannie Mae and Freddie Mac have enough capital, according to the companies, is to subject them to "stress tests" simulating adverse economic conditions.

Fannie Mae's current capital cushion can absorb losses equal to 8.5 percent of its mortgages defaulting, which is essentially what happened in Texas in 1981 and 1982, Jeffers said. Enough capital would still remain to sustain the company if interest rates rose a full 6 percentage points in one year without falling for another four years.

Freddie Mac's stress test indicated that it would not lose money even if economic conditions paralleled the prolonged decline in houses prices and rise in unemployment that marked the Great Depression, Allen said. Specifically, Freddie Mac would not lose money even if house prices fell 40 percent over four years, interest rates rose sharply and stayed high for 10 years and the company attracted no new business over those 10 years.