The Treasury Department's tax reform package released earlier this week would have significant impact on real estate -- and not simply on the big bucks syndicators, developers and investors whose lobbies make the most noise on Capitol Hill.

An examination of the proposal, in fact, turns up several key areas where ordinary, moderate-income families renting or seeking to purchase new or rehabilitated housing could pay a steep price for tax reform.

The largest group of losers probably would be the estimated 200,000 first-time home buyers per year nationwide who obtain mortgages at discount interest rates through state and local housing agencies.

Under the Treasury's plan the supply of 9 to 11 percent mortgages regularly made available to new buyers through tax-exempt bond issues would dry up permanently on Jan. 1, 1986. On that date, Treasury would deny federal tax exempt status to the underlying bonds that finance new cut-rate mortgages. That, in turn, would stop investors from sinking any additional dollars into the bonds at below market rates.

Over a period of just several years, tens of thousands of families who might otherwise have qualified for a home loan at the cut-rate, tax-exempt costs would either be forced out of the market altogether, or be forced to wait and hope for some form of state or locally funded replacement.

That is precisely what Treasury urges governments such as Maryland, Virginia and the District to do.

"If below-market mortgages . . . are thought to be worthy of local support," said the Treasury's report to the president this week, "they should be financed locally, not through inefficient federal subsidies . . . that drive up tax rates throughout the country."

Treasury offered no specific suggestions on where local revenues for the estimated $11 billion to 12 billion per year worth of home mortgage money currently raised through tax exempt bonds would come from.

The department was emphatic however that the money shouldn't come directly or indirectly from federal coffers.

Moderate-income homebuyers would not be the sole casualties of Treasury's proposed tax exempt financing bust. Tens of thousands of lower and moderate income tenants across the country would also be affected.

Though the program rarely draws publicity and many of its own beneficiaries have never heard of it, tax-exempt financing accounts for a major chunk of new construction of moderate income rental apartments.

According to General Accounting Office figures, $6 billion worth of cut-rate apartment loans were financed via tax-exempt bonds in 1983. Substantially higher totals are projected for 1984 and 1985.

By law 20 percent of the units in every project financed through locally issued bonds must be made available to lower income residents. Since Congress and the Reagan administration have cut back sharply on direct federal housing subsidies during the past four years, tax-exempt-bond-financed apartments represent the sole source of new construction of rental units in many parts of the United States.

Under Treasury's package, tax exempt money for moderate income apartments would become disappear on Jan. 1, 1986.

Still another key consumer related housing sector that would suffer under the Treasury's proposal would be rehabilitation of historic buildings and conversions to rental property.

Thanks to the 25 percent investment tax credit (ITC) for certified historic rehab that Congress made available three years ago, conversions of under-used, deteriorating or abandoned structures into rental housing has boomed.

The National Trust for Historic Preservation estimates that during each of the past two years, over $2.1 billion worth of rehabs have been stimulated by the existence of the investment credit. Close to 60 percent of that has gone for renovation of dwelling units.

Terminating the credit -- along with other incentives for preserving non-historic commercial and industrial properties -- would be "an outrageous waste of national resources," in the words of William Langelier, head of a Boston- and Washington-based firm active in financing renovations.

The National Trust itself in a letter to President Reagan this week quoted words from a speech Reagan himself had made last Sept. 18 during the campaign. In the speech, the president lauded the rehab credits as "a major innovation that our administration put into effect."

Unsubsidized, market rate home buyers might be yet another loser under the Treasury plans unveiled this week. A little noticed, technical sounding section of the proposal calls for changes in "installment sale" tax treatment.

The net effect of the changes would be to eliminate the rapid spread of so-called builder bonds. Home builders use these taxable bonds to finance home loans themselves, often saving their purchasers interest charges in the process. The Treasury dislikes the technique because home builders spread out their tax liabilities on the financed houses over a period of years.