'It's been a steady stream like this all day," the young real estate sales agent laughed, stepping forward to hand a sales brochure to a couple just entering the front door.

The scene: a spacious, two-bedroom condominium "garden apartment" in the Lincolnia section of Fairfax County in northern Virginia. The reason for the press of visitors, the real estate agent noted, could be found in the unusual selling price. At $49,000, the condominium was roughly half the average cost of houses in the Washington area.

And what's happening in Washington -- and at the Lincolnia condominium -- largely has been true throughout most of the United States this summer.

Although the housing market has managed to hold a relatively steady course this year -- despite rising interest rates, a recession and escalating home prices that now average $74,000 for a new home -- housing experts see a number of signs that could point to a downturn in 1980.

Industry officials are watching these signs carefully, keeping a wary eye glued on what happens to the overall economy during the next few months, particularly the effects of recession.

"We're now projecting 1.6 million (housing) starts this year," said Michael Sumichrast, chief economist for the National Association of Home Builders.

And that, Sumichrast said, is "not bad," considering rising interest rates on one hand and inflation on the other.

For 1980, however, the home builders' association has just revised its projections downward for the third time this year. According to Sumichrast, 1980 starts probably will drop to around 1.5 million, compared with more than 2 million new housing units in 1978.

A severe recession, he said, could quickly change the 1980 forecast, since "people will just stop buying" in a deep recession.

Sumichrast noted another troubling concern. Thrift institutions (savings and loan associations and mutual savings banks, which together finance a substantial segment of the U.S. housing market) have been seeing a sharp drop in savings deposits during the past five months, as more and more savers are transferring savings accounts in banking institutions to money-market funds.

According to officials of the U.S. League of Savings Associations, the net inflow at savings banks increased only $1.5 billion during July 1979, compared with $2.9 billion in July 1978.

At mutual savings banks, meanwhile, the outflow (withdrawals) of deposits hit $275 million in July. Moreover, the 1979 withdrawal rate was disturbingly close to the outflow of $733 million in deposits in July 1974, during a sharp economic slump.

For the seven months through July 1979, the loss in savings deposits from mutual savings banks hit $2.2 billion -- a much sharper decline than the outflow of $59 million during the first seven months of 1978.

Regardless of deposit losses from savings institutions, housing officials note, ample mortgage money still is available.

Moreover, lenders are now offering different types of graduated and variable-rate mortgage plans.

National economic analysts tend to agree that, all factors considered, the housing industry should be able to avoid any deep slump in home construction in 1979 and 1980.