U.S. taxpayers are facing another bailout.

If a private company can't be found to take over the troubled Higher Education Assistance Foundation (HEAF), which provides government-backed student loan guarantees, the U.S. Treasury will confront and estimated $1 billion to $2 billion in losses. The chairman of the agency already has been forced to resign.HEAF is one of two guarantee agencies operating nationwide. Its purpose it to encourage banks to make unsecured loans to college students.

Almost since it was established in 1976, HEAF loan guarantees have gone overwhelmingly to students attending so-called proprietary (for-profit) trade schols - the kink you see advertised in magazines and on TV: Wanna learn to drive an 18-wheeler? Be on radio? A computer programmer?

Many of these schools are first rate. But too many of them, investigations have shown, are student-loan mills. Indeed, HEAF launched a vigorous marketing campaign in the 1980s to extend its businesses and now guarantees a majority of loans to sutdents attending such trade schools.

The problem is that of HEAF's $9.6 billion loan protfolio, nearly 60 percent of its business comes from propriety schools- about $5.7 billion!

Although the U.S. Education Department has not released figures on how much of that $5.7 billion is considered at risk of default, past history is not encouraging. Nationally, default rates as hight as 80 percent exist among some trade schools, with numbers in the 40 percent to 50 percent range not considered unusual.

One of the HEAF's jobs is to see the loans are paid back. Implicit in a guarantor's job are its responsibilities to recognize troubled schools and judge the integrity of the schools to which students seeking loans apply.

Unfortunately, HEAF has not done a good job of policing the trade-school industry - guaranteeing loans, for example, to countless "students" pulled off unemployment or blood donor lines by school recruiters.

While this is bad enough, worse is Congress's reaction. Not only did Congress write the law creating HEAF, it has been HEAF's biggest protector and defender.

Keep this in mind: HEAF doesn't print its own money. It uses tax dollars to fund its misadventures. And its nearly 1,000 staff members are handsomely reimbursed, receiving a 1 percent commission on the amount of each loan it guarantees and an additional 3 percent on every loan that the government pays recipient institutions.

As a result, though the agency has been granted non-profit status, it has amassed extensive assets. According to its own annual report, it "finished fiscal 1989 with net current assets of more than $100 million, a combined total fund balance of $139 million and total assets of more than $1 billion."

The broader question, of course, is this: Why are taxpayers subsidizing fly-by-night trade schools? The problem is not with the students who attend them but with the schools themselves; many of them simply do not deliver the services promised.

Congress in the end may very well bail out HEAR. But maybe we schould just let the market take its course and let HEAF pick up the tab for making bad loans.

The worst that could happen is that HEAF would have to seel off its assets, spend its reserves and go out of business. Maybe Congress would then take a serious look at the trade-school loan scam and the system that has made it possible.

(Jeanne Allen, a former U.S. education department official, is education policy analyst at the Heritage Foundation in Washington, D.C.)