THOSE TAX-EXEMPT bonds that many states and some cities are using to provide funds for low-cost, single-family mortgages do have their appeal. Local housing experts all over the country, as well as some political leaders, are up in arms at the possibility Congress may abolish or sharply limit them. Some concede limits are needed on the way tax-exempt money is used by fear Congress will be too restrictive. Others, like Virginia Attorney General Marshall Coleman, regard any congressional action as inappropriate although few put that objection in the language of states' rights as he did Wednesday.

The irony in Mr. Coleman's position is that it seems clear state and local governments are on their way toward taking over the entire home-mortage market unless Congress does something. Such a development would be more at war with traditional concepts of a free-enterprise system than congressional action would be with the concept of state's rights.

A recent study by The Urban Institute reports that in communities where these bonds have been issued, they account for roughly 30 percent of local mortgage lending. In two communities - Pueblo, Colo., and Pine Bluff, Ark, - the tax-exempt share of all mortgage financing is now approaching 100 percent. The political appeal of this mechanism - which enables some buyers to get mortgages at 7 or 7 1/2 percent instead of 9 1/2 or 10 - makes it difficult for local officials to draw and enforce lines between low and moderate, or moderate and high, income families.

The fundamental policy question now facing Congress is the extent to which any government - federal, state or local - should get into the business of helping citizens obtain the kind of housing they would like to have. As long as tax-exempt bonds were used to build public housing, subsidize the purchase of cheap houses by low-income families, or even build rental housing for moderate-income families, no one complained or worried much. But now that these funds are being used to provide cheap mortgages on $50,000 or even $100,000 houses, the whole idea of using tax-exempt money for housing is being questioned.

The solution may be for Congress to force these tax-exempt bonds back to where they originated. That, unfortunately, would deprive state and local governments of the most effective system they now have to rehabilitate run-down portions of cities or provide a mix of residential housing in high-income areas. But there are other ways of handling those situtions, like direct subsidies, partial interest refunds and, above all, lower mortgage interest rates and less inflation.

These may not be as effective, (or politically popular) as the new cheap mortgage game. But they do not have the advantage of posing fewer threats to the credit ratings of local governments, the federal treasury, and the traditional role government has had in meeting the financial problems of citizens.