An intriguing new real-estate investment concept is under consideration on Capitol Hill as part of the 1990 tax bill: a tax credit that would simultaneously save the government money on its savings and loan cleanup efforts, and attract equity dollars from investors who would otherwise never touch "distressed" real estate.

The idea is dubbed the "RTC credit." RTC stands for the Resolution Trust Corp., the federal agency responsible for disposing of the assets of dead, dying and sick S&Ls.

The RTC's real estate portfolio consists of $17 billion worth of properties but could eventually total several times that amount, S&L experts said. Though some of the properties are readily salable, the majority are not. In a full year of effort, $2 billion worth of real estate has been sold by the RTC, the officials said.

Meanwhile, new properties drop into its portfolio daily, as the federal government takes over additional S&Ls and clears titles on foreclosed real estate. Critics in Congress and in the industry -- notably the 800,000-member National Association of Realtors -- say RTC hasn't been fast enough or imaginative enough to move its huge stock of houses, apartment and office buildings, shopping centers and land.

A partial answer: the RTC tax credit. Patterned after the low-income-housing tax credit, the RTC credit would give private investors new incentives to put money into cleanup real estate. It would also cut the RTC into the potential upside of the deal by sharing resale or refinancing profits down the road.

The low-income-housing tax credit has enjoyed bipartisan support in Congress, plus Bush administration backing. The program has stimulated construction of 111,000 new low-rent units and the rehabilitation of another 95,000 units in its three-year existence, according to the Department of Housing and Urban Development.

The tax-credit concept works like this: If you put your money where Congress wants you to, you get a credit on your federal tax bill -- a dollar-for-dollar reduction of what you owe at the bottom line. The function of the credit is to cut your risk of taking a financial bath in an inherently high-risk but socially desirable venture.

The RTC credit proposal is now before the Senate Finance Committee and the House Ways and Means Committee. It would allow purchasers of certain RTC real estate to take tax credits over five years equal to as much as 80 percent of the equity they put into the property. The credit amount would be determined by subtracting the mortgage financing from the purchase price of the building.

For example, a $500,000 building bought from the RTC with a $200,000 mortgage would require $300,000 in equity from investors. The same building might well have been appraised at $1.5 million four or five years before. Under the credit concept, the purchasers could cancel out $240,000 (80 percent of $300,000) worth of their regular federal taxes in equal installments over a five-year period.

During this period, they would renovate the property, attempt to restore it to full economic viability and maximize its capital value. At the end of five years, they could refinance or resell the building for whatever they could get.

If they bought right, managed right and sold right, the property might be worth $1 million. The investors would then share 80 percent of those profits among themselves, and write a check for the other 20 percent of the profits to the RTC. The latter feature is called an "equity kicker." Once the RTC sells the property, it's permanently off the government's books as a liability. But if the property makes money, the government gets a one-fifth piece of the action.

A team of four economists headed by RTC consultant John Urbanchuk estimates that even with the revenue losses of a credit like this, the net savings for every $1 forgone by the government would be $2. That's because the costs of keeping real estate assets on the RTC's books are so steep -- often 3 percent of appraised value per month. The costs include maintenance, real estate taxes, utilities and insurance.

The RTC credit is the brainchild of Boston investment banker John P. Manning and Washington tax attorney David H. Miller. Manning's firm, Boston Capital Partners Inc., is one of the largest financiers of low-income-housing tax credit properties. The likely minimum investment in an RTC credit deal, according to Manning, will be $50,000.

Key members of the Senate Finance Committee, including Sens. David L. Boren (D-Okla.), William A. Armstrong (R-Colo.) and William V. Roth (R-Del.), have indicated that they back the plan, as has Rep. Clay Shaw (R-Fla.) of the House Ways and Means Committee.

Action on the 1990 federal tax bill is expected to occupy Congress through September.