The American appetite for home ownership, whetted to an unusual degree in recent months by investment fever, may be substantially dulled as housing prices and financing costs continue to climb.

Housing demand is always difficult to analyze. When it's hot, we know it because people are able to buy and mortgage rates are acceptable; when it cools, the reverse is true.

The depth of housing demand on a given day is also difficult to perceive, mainly because it is related to the personal situations of those interested in ownership. The money for a downpayment may suddenly become available, or a pay raise may make montly payments affordable

Young couples tend to think more seriously about ownership when a baby is born. Older couples tend to think about living some place else after children are grown or when retirement is being planned.

There is also a substantial group of middle-aged owners who think about buying something newer when their mortgage payments - and subsequent tax deductions for interest - are shrinking.

Housing demand has been unstable during the past decade. It tends to run hot or cold. The tepid period is like spring in Washington - a brief break between winter and summer.

Because the housing marketplace here during the past 18 months has been buzzing with eager buyers, there has to be some apprehension as to how much longer the "up" market can last. Mortgage interest rates have increased nearly 1 percent in less than a year and now are nudging the usury ceiling of 10 percent in the District and Maryland.

Several days ago the FHA-VA rate ceiling was raised to 9 percent, but the common rate for privately financed loans now is 9 3/4 percent - if the down payment is substantial.

But there now is mounting fear among all realty and building professionals that the supply of available mortgage funds is shrinking as normal loan sources are either temporarily shutting off or doling out their loan money as the result of a present shortage or fear thereof. And, if interest rates rise more, there is a possibility that most of the available money would go into Virginia loans because there is no usury ceiling there. That's what happened in 1974, when money was tight and expensive.

Meanwhile, prices of resale and new houses have been rising here faster than in most other areas of the nation. Price tags and financing costs are known to affect all potential buyers, especially those categorized as "discretionary," because they already own a house or have a satisfactory rental apartment or town house. After looking at houses offered in the market, they can decide to stay put for awhile longer.

Prof. R. L. Skrabanek of the Texas Real Estate Research Center at Texas A&M University, noted in a recent Realtor Review publication that the number of households nationally is expected to increase by 12.5 million in the next eight years. This average annual net increase of 1.6 million between 1977 and 1985 "is 33 percent higher than the average annual net increase between 1970 and 1977," he pointed out.

Skrabanek used those figures to predict that housing demand in the United States will remain strong through 1985, with the number of households growing at a faster rate than the population.

While that projection should encourage home builders and homeowners planning to sell, economist Leonard Santow predicts that housing starts will continue strong into summer but will ebb in the last half of the year and bottom late in next year. Starts then are expected to number 1.5 million, in contast to the 1.8 million total expected this year and the 1.98 million level achieved in 1977.

Speaking in Annapolis at a seminar for news people arranged by the National Association of Home Builders, Santow based his short-range pessimism on rising interest rates, a lessening of available mortgage funds, an unusually large federal deficit that will trigger heavy Treasury borrowing in the second half of this year. Fears of high-priced labor contracts in 1979 should also contribue to this, he said.

Santow, The senior vice president of J. Henry Schroder Bank & Trust Co. in New York, sees "at least a mini-recession" next year before housing starts rebound to the 2 million level in 1980.

Other observations at the session:

Housing was the "biggest single missing piece" in President Carter's recent urban policy outline, according to John J. Gunther, executive director of the U.S. Conference of Mayors.

Washington area builder Martin Poretsky said that the costs of "bricks and mortar" going into the average house increased only minimally, percentage-wise, in the last 20 years.