The Treasury Department has run up the white flag on 1984's most controversial issue affecting American real estate: the so-called "imputed-interest-rate" provisions of this year's federal tax reform act.

In an intensive, 10-day series of meetings with congressional and industry groups, Treasury negotiators agreed to an eight-point compromise pact designed to relieve tens of thousands of property owners, sellers and buyers across the country.

Whether or not Congress passes the compromise before the end of the 1984 session, the draft package agreed to in closed-door conferences last week is highly significant. It means that the authors of the imputed-interest concept -- a set of tax law changes that would raise effective interest rates in large numbers of property transfers -- have conceded that their reforms are politically untenable. It means, too, that the imputed-interest sections added to the federal tax code this July almost certainly will be revised, if not repealed outright. Precisely when and in what final form the revisions will be adopted were still uncertain as Congress groped its way toward adjournment following the Columbus Day recess.

The imputed-rate imbroglio, which triggered an estimated 40,000 pieces of mail to Capitol Hill over the past several weeks, centers on the "true" interest rates charged by sellers of single-family homes, farms and other real estate. For decades, property sellers have made real estate more attractive to potential purchasers by offering cut-rate financing terms as part of the deal. For example, the seller of a home or duplex might offer to "take back" a mortgage at 10 percent for 10 years as an inducement to the buyer. Sellers of far larger properties -- from shopping centers to downtown office complexes -- have done the same.

The Treasury Department, however, long has argued that cut-rate financing amounts to a tax dodge. Sellers of real estate inevitably get higher sale prices when below-market financing is attached, Treasury revenue experts have said.

The extra high prices, in turn, result in larger capital gains to the seller, taxable at low rates. Had the higher prices been treated for what they truly are -- that is, deferred-interest payments padded onto the price to compensate the seller for subsidizing the mortgage rate -- the government would have higher revenues, in Treasury's view. The interest income to the seller could be taxed at ordinary rates, far higher than capital-gains tax rates.

The 1984 federal tax legislation incorporated a comprehensive system for putting Treasury's view of all this into operation next Jan. 1. Under the still-unofficial compromise plan hammered out last week, though, Treasury said it would accept the following rules:

*Seller financing of principal residences and vacation homes with purchase prices of $250,000 or less would use a straight 9 percent imputed-rate standard.

In other words, if you sold your vacation house and took back a note at 9 percent or more, you'd have no worry about Uncle Sam. If your note rate were 7 percent, the tax man would impute or assume that your true rate was 9 percent.

*Principal homes or vacation homes selling for more than $250,000 would receive a "blended" imputed rate. The portion of the sale price in excess of $250,000 would be treated as having a true rate equal to 100 percent of the current rate for Treasury securities of comparable maturities. (On 10-year notes at present, that would work out to roughly 13 percent.)

The portion of the price under $250,000 would be treated as having a 9 percent rate. The two rates then would be blended on a weighted basis to come up with a composite imputed rate for tax purposes.

*Farms or ranches with sale prices of up to $2 million would get 9 percent imputed-rate treatment. Everything above $2 million would be subject to rate blending, as in sales of principal residences and vacation homes.

*Small businesses selling for $1 million or less also would qualify for 9 percent imputed-rate treatment. On sales above $1 million, the weighted-blend rule would apply.

*Investment properties selling for $4 million or less would be subject to imputed rates equal to 80 percent of the comparable rate for Treasury securities. Currently that comes to an effective 10.5 percent rate standard. Deferred payment amounts over $4 million would face the 13 percent standard.

*All existing cut-rate loans assumed or taken over prior to adoption of these compromise rules would be grandfathered -- that is, exempted from worries about imputed rates. Loans assumed after adoption of the rules, on the other hand, would be covered