Despite the increasingly affluent appetite for housing ownership here and elsewhere in the nation, this year's production and sales of new houses and resales of existing dwellings will be 20 percent to 30 percent below those market figures for 1979.

The fundamental reason is simply that mortgage and construction interest rates rose at an unprecedented pace a year ago, moderated in early summer and then began another upward move in late summer.

These additional costs of both short- and long-term borrowing in all housing-related areas have diminished sharply the abilities of both small and large firms to build and have lessened the ability and the incentive of discretionary purchasers to make positive buying decisions.

In addition to the usual incentives to have tax deductions for mortgage interest and property taxes, only a long-nurtured confidence in the rising values and prices of area dwellings have kept this housing market moderately vibrant through most of the past year. Essentially, that confidence is based on the indisputable fact that almost every house sold here eight or nine years ago now is marked for resale at a figure double the selling price in 1972. Average prices here rose from about $40,000 to $80,000 for both new and resale houses.

Thus, the reasonable tendency is for today's prospective purchaser to assume that the $100,000 dwelling purchased now will be resalable for $200,000 in 1990, if not earlier.

That asssumption also is based on a continuing general inflation rate that appreciating housing values and prices have exceeded over the past decade.

A recent study by Avance Mortgage Corp. indicated that starts of single houses will decline this year to the 13,000 level, about 25 percent below the production achieved in 1979. The study additionally pointed out that sales of town houses and small single houses in the range under $120,000 are selling well, and that town houses and condominium apartments priced under $75,000 find buyers who can qualify for ownership.

However, there has been a noticeable softening in the condominium market for units priced over $150,000 and for both new and resale single houses with price tags exceeding $175,000.

Somehow, the financial ability and the need for increasing income tax deductions for interest and taxes keep the almost unreal market fairly strong in the range from $200,000 to nearly $600,000. However, there are also some solid opinions that the number of new dwellings built for sale above $400,000 may be exceeding the number of potential buyers here.

Expectations for ongoing solidarity and appreciation in area-wide housing prices are, to some degree, based on lowered production in the past two years and prospects for only a slight upturn in 1981. Nationally, this year's new housing production in the private sector is expecting to be less than 1.2 million units. That compares with 1.75 in 1979 and a projected 1.4 million in 1981.

For the hard-pressed housing-production industry, which experienced an even more debilitating decline in 1974-75, the small solace in the current market is the lack of overbuilding in the lower price market ranges. The inventory of unsold houses generally is less than half of what it was in 1975.

There are some forecasts that mortgage rates will steady or ease slightly by the end of this year. But those same forecasts anticipate another rise in 1981. Therein lies the basis for the likelihood that new housing production and reselling may have to cope with unfavorable financing terms for months to come.

However, it's also possible that a lessened demand for higher-rate mortgages may quickly result in another downturn in rates this fall and winter if housing sales tail off and buyers are either unable or unwilling to accept long-term mortgage rates in the above-13 percent range. That's exactly what happened last winter.