A market assessment prepared for the District in 1981 projects that as many as 12 million square feet of new office space could be built by 1984 but concedes there will be a demand for only 5 million square feet in that period.

The study, which was done by Tischler, Montasser and Associates Inc., also forecasts demand for 17.3 million net new square feet of office space downtown by the year 2000. District officials project an additional 25.6 million--TMA's estimate of new space requirements for the entire District by the end of the century.

TMA essentially projects a more conservative demand for general-merchandise retail space as well in the next 17 years.

A copy of the economic and planning consultants' study was made available to The Post after a recent Capital Commerce column questioned development trends in the downtown core.

TMA's more conservative forecast of space demands over the next decade and beyond takes on added significance in light of several development issues that have received little public notice.

A principal development issue is the "fragmented ownership of the downtown retail establishment," according to the market assessment by TMA.

The retail core referred to in the study is defined as F Street NW, with Woodward & Lothrop at the eastern boundary and Garfinckel at the western. It is the core of Washington's traditional downtown area, bounded by Pennsylvania Avenue to the south, 15th Street on the west, Massachusetts Avenue and M Street on the north and North Capitol Street on the east.

Unlike shopping malls that operate under a single leasing authority and strategy, the retail arrangement downtown may go through several cycles until a suitable mix of department and specialty stores catering to all income levels is in place, TMA noted.

What's more, it concluded that any benefits associated with a strong retailer situated at either end of a retail core will decrease if the retail frontage is interrupted. Disruptions could be caused either by nonretail or inappropriate use, "or extensive mini-malls, which threaten to siphon off or discourage the maximum pedestrian traffic between the two anchors.

"An overall uncoordinated retail approach will make it even more difficult for an appropriate retail mix to be achieved" in that core, TMA cautioned.

Another development issue to be considered is the increasing cost of rent. As office leasing rates increase, retail establishments will find it more difficult to pay the rent unless they are high-volume concerns such as fast-food restaurants, TMA predicted.

TMA further cited the likelihood of a trend in an improved retail core toward the sale of general merchandise to moderate- and upper-income households. It said "this has serious implications" for the lower- and moderate-income patron, "not only because of the stores which are likely to be replaced but also due to the lack of major discount retailers who cater to this segment of the market."

Based on that assumption, TMA suggested that sub-areas outside the downtown core should be evaluated to determine the feasibility of providing moderate- and lower-priced goods for some segments of the population.

In any case, TMA estimates that resident, employe and tourist spending in the primary trade area east of 15th Street NW would support 1.9 million square feet of retail space by 1985, assuming that a new Hecht's will be built at Metro Center. A more optimistic assumption that anticipates the addition of a fourth department store in the retail core projects demand for 2.3 million square feet.

Both scenarios assume sales volumes of $200 a square foot for retail establishments in the primary trade area.

The major issue affecting development of office space downtown is the desire to provide for other land-use activities, TMA asserts.

If downtown were to be developed as Rosslyn was, "The future viability of downtown as the primary office market in the metropolitan area could be challenged," the TMA study concludes.

As office space is developed downtown and as suburban locations achieve a greater critical mass, "It is imperative that the downtown be regarded as a 'living downtown,' " it emphasized.

Estimates and projections by city officials and private developers differ with the TMA analysis in varying degrees. There is full agreement, however, on at least one issue: The public and private sectors should join forces to make the area in question a "living downtown."