Home buyers are finding new dwellings increasingly hard to afford in this area, where average prices in subdivisions have zoomed by 18 percent in the past year.

Prices of new single-family houses now average $98,500, an increase of 14 percent over last summer, while town houses and one-over-one town houses and apartments are averaging $81,000, up 32 percent in one year.

Not surprisingly, there are indications that the market is strongest for houses -- and new and converted condominium apartments -- in the lower price ranges. Unit sales of condominium apartments increased by 35 percent in the past year, while other sales of new dwellings were off 10 percent. The number of resales also declined slightly in the first eight months of this year, but dollar volume is up slightly.

No doubt about it, the rising prices of all new homes and the upward swing of effective mortgage interest rates -- to 11 to 12 percent for conventional loans and to 10 percent for FHA-VA loans -- are pinching the buying power of eager first-time buyers and cooling the interest of trade-up purchasers. The latter group, which accounts for nearly 70 percent of the new home market, typically takes advantage of equity in present homes to buy something newer and/or larger -- and likely more expensive.

If there's any discernible build-up in the inventory of unsold houses, it's among the detached houses priced at more than $120,000. Conversely, the hottest selling single-family houses are those priced under $100,000.

Town houses, which have attracted more buyers in recent years, are reported selling well generally, but especially those priced under $70,000.

"Our survey shows that the inventory of all unsold subdivision homes is about 2,600 -- and that's considered low because it's less than a 1 1/2-month supply in this market," said Deborah Rosenstein, an analyst with Housing Data Reports, which keeps tabs on projects with more than 40 units.

She added that the inventory of unsold new and converted condominium apartments is even less extensive because of exceptionally strong sales in recent months.

However, HDR surveys do not include the output of the hundreds of small-volume builders. Those builders tend to specialize in custom (built for a specific buyer) and speculation (built without a specific buyer in mind) houses. Often their houses are completed without being under contract, in contrast with the current practice of large-volume builders. Informal reports indicate that an increasing number of these homes are available for purchase now.

Nor do surveys show the number of expensive houses that have been started without benefit of sales deposits from prospective purchasers. Yet, it must also be recognized that some higher-range builders consistently gear their output to have a few houses ready for nearly immediate occupancy -- to capture the "want-to-move-in-tomorrow" market.

In recent interviews, area housing professionals unanimously discounted the possibility of a large investory of unsold houses, because builders still remember the slowdown in sales and resulting glut of unsold houses that developed in the downturn cycle that began in the summer of 1973. Then mortgage money was expensive and difficult to find. Now mortgage money is even more expensive but it's still moderately available.

However, one veteran developer said that an inventory of unsold houses might develop in the relatively few subdivisions where the builders are young enough not to have been in business themselves in 1973-74.

Builders who survived that earlier "down" market have insisted that they would never again start more than a few houses ahead of their selling pace. In fact, most of the large-volume builders want to have a sales deposit in hand before a house advances beyond the foundation stage.

While the volume of prospective buyers of new and resale houses decreased more than seasonally in the muggy, vacation days of July and August, builders and their selling agents insisted that "those who looked were really serious about it."

Katherine Olmstead, a marketing executive with Long & Foster, a realtor firm that handles new and existing home sales, said that resale houses "are on the market a few weeks longer but they sell if they're clean.

Olmstead added: "The overall housing market itself is not nearly as bad as the general economic news about interest rates and fears of a recession." She agreed that town houses are selling faster than single-detached dwellings.

One reason is that more town houses are available in the price range of more buyers. However, the sales of expensive town houses in close-in locations -- such as Falls Church, McLean, north Arlington, Old Town Alexandria, Northwest Washington and Chevy Chase-Bethesda -- have been consistently good.

Additionally, because of prices below the market average for detached houses, town house sales have been active in Laurel, Seabrook, Burke Center, Columbia, Newington Forest and other farther-out locations where the longer commuting distances are overbalanced by price and product incentives.

In July, there was general concern in housing about obvious effects of the gas shortage on the inclinations of purchasers. Traffic declined sharply for several weeks when gasoline lines were the No. 1 topic of most conversations. Now gas stations are open again and the decision to buy and how far to commute is more likely to be equated against the current price of gasoline and any fears of still-higher prices or another pinch in supply.

Another area of concern is mortgage money, now at all-time-high interest rates. That should bode good for the supply of mortgage funds and has brought some new investors into that field.

But a veteran mortgage banker would tell you that a look at the 11-plus percent rates being advertisied for six-month mortgage certificates in the $100,000 category is evidence that savings and loan associations need funds to make more loans and that those loans must be priced at least 1 percent higher to make the transaction worthwhile for the conventional lender.

"Nothing in today's market picture indicates mortgage rates can go anywhere but up for a while," said James Latta, a mortgage executive with DRG Financial Corp.

On a national basis, economist Kenneth Biederman of the Federal Home Loan Bank Board said that he expects mortgage rates to decline to about 11 percent by the end of this year and to the 10.7 percent level by mid-1980. But he cautioned: "Remember Washington area rates are always above the national average."

Walter Mess, president of the area Mortgage Bankers Association, said: "I think mortgage rates have already peaked and will move downward slightly within the next six months."

Some realty professionals insist that the level of mortgage interest rates no longer matters in terms of psychological barriers to buyer. But the same pros also recognize that every rise in interest rates takes some prospective buyers out of the market for economic reasons. The same holds for increases in prices of houses.

Yet, there also are sound reasons to expect some softening in the rise in prices of both new and existing houses if demand slackens. And a lesser demand for mortgage funds could reasonably be expected to soften those high interest rates in future months.

Meanwhile, the National Association of Home Builders continues to emphasize a decline in new home sales and growing national inventories of unsold new units. Nationally, housing starts are expected to sag in the second half of this year and remain sluggish through much of 1980.

Even the normally ebullient National Association of Realtors, whose members handle most of the houses resold throughout the nation, has indicated a downturn in resales and recognition of Commerce Department statistics that the total U.S. economy is in a recession.

But no immediate recession is perceived in new or converted condominium apartment sales by G. V. (Mike) Brenneman, whose real estate firm here has specialized in condo sales and resales and conversions. He wrote recently about "an unprecedented surge in buyer demand for multi-family ownership," adding that the demand is expected to continue strong for five to ten years.

Why the turn to condominium ownership, which had a hard time catching on here in the early 1970s?Brenneman cites several familiar reasons: the maturing of World War II babies into a potent market force and thus more one- and two-person households in cities, more empty-nesters among senior citizens, more divorced persons and thus more households, relatively higher levels of affluence in the middle- and upper-income groups and broader endorsement of a life style tailored more to leisure than to home maintenance chores.

Acceptance of condominium ownership and living in high-rise and garden-style buildings has increased markedly in this area. One reason is simply that these multi-family units have become more attractive to prospective buyers

But don't write off the future of the single-family house. That's been

But don't write off the future of the single-family house. That's been done before -- prematurely, it turned out. The single house remains the goal, according to housing surveys, of more than 90 percent of American households.Now many persons are entering home ownership through the condominium door. Then it's a move up to a town house and then to a detached house. That's the pattern of the 1970s in this area.

Interestingly, for statistical purposes and even in the minds of many buyers, the town house is now regarded as almost synonymous with "single-family." Also, there is increasing public interest in ownership of a so-called mobile house, usually settled on a permanent site owned by the occupant. When and if the first area developer proves there is a strong market for permanently sited mobile (often called "manufactured") houses, the housing market will extend to people who can't afford more than a two-bedroom condominium town house, garden apartment or one-bedroom condo in a high-rise. The overall housing market itself is not nearly as bad as the general economic news about interest rates and fears of a recession.

But you may be antsy about becoming a homeowner in a slightly recessive economy that you fear might turn into something far worse. In other words, will there be a big real estate shakeout and market collapse in this metropolitan area? Almost all professionals say no, but they also agree that some "leveling or adjustment" from continuing high rates of inflated housing prices is overdue.

If you look to the past for an answer to fears about a major depression, you have to go back to the 1930s. And there was a major recession -- the worst economic downturn since the depression -- in 1974-75.

But this city survived much better than most. World War II brought more people to this area and that growth trend has been enlarged by subsequent events in the 1950s, 1960s and 1970s.

Meanwhile, realty and building veterans remember that there were both down and up cycles in the three decades since WWII. The housing market went cold twice in the 1960s and a redhot market of the early 1970s was thoroughly chilled five years ago.

But did housing prices plummet? No, they bottomed out and declined slightly. A glut of unsold new condominium apartments got hurt most. There were some foreclosures and some builders lost their silk shirts and their way of life. But the market bounced back in 1976 and gained even more inflationary momentum in 1977, 1978 and the early part of 1979.

Now another adjustment period may be starting here. Depending on the general economy, the housing shakeout could be mild or fairly severe and short or moderately long. Almost to a person, most professionals agree with condominium-co-op specialist Edmund C. Flynn, who answered a question about a possible major real estate price downturn this way: "Not unless inflation is totally licked."

In recent years, residential real estate appreciation has led the rate of annual inflation by several percentage points. Residential ownership has increased and so has private investor ownership of dwellings that are rented to tenants.

If this area's population growth declines considerably, realty prices might move down sharply. Most persons in real estate (and that includes so many people these days) feel that a moderate adjustments in escalating prices is to be expected. But not a major downturn in this national capital area.