Notwithstanding the current upsurge in home buying activity, the American dream of home ownership is in jeopardy, a special task force of the United States League of Savings Institutions warned this week.

"We found that the economic realities for home buyers are nowhere near as bright as the conventional wisdom suggests--and that the much-ballyhooed 'recovery' is far more fragile than the prevailing popular perception," the task force said.

Citing continuing problems of capital shortage and affordability, the task force concluded that the outlook for home ownership through 1990 is a sobering one.

The pessimistic outlook was contained in a report by 24 officials of saving institutions who were charged by U.S. League Chairman Leonard Shane with studying ways to restore affordable home ownership as a high national priority. The U.S. League has more than 3,500 savings institutions and savings banks as members.

Among the report's conclusions:

* A drop in the ratio of home ownership in the United States since 1980--the first drop since the 1940s--has wiped out half the gain in the 1970s. According to the U.S. League, the share of American households owning their own homes dropped to 64.8 percent in 1982 from 65.6 percent in 1980. The home ownership ratio had been rising steadily since the end of World War II.

* Even under a sanguine interest rate forecast, housing affordability will continue to be a severe problem for a large percentage of would-be buyers. By next year, even if median home prices remained constant at 1982 levels and mortgage rates drop to 11 percent--both considered unlikely--there would still be a $14,000 gap between the price of the median-cost new home and the amount a typical first-time buyer could afford to pay.

Not all Americans are affected, but the home ownership outlook was called "dreadful" for some segments of the population who've had little ownership opportunity in the past, including lower-income families, the elderly and handicapped, and minorities.

* A "demographic mismatch" will limit the rate of savings accumulation in the economy overall and reduce the availability of lendable capital for home mortgages. The mismatch will result because of a more rapid growth in the number of people entering the prime borrowing ages (25 to 44) than in the number of Americans who will be in the prime saving ages (45 and older).

* The prospect of a severe capital shortfall for the economy as a whole continuing through the remainder of the 1980s will have a negative impact on housing. For this, the group placed blame largely on "the inability of Congress and the administration to exert self-discipline and control over the size of federal budget deficits." The deficits require the federal government to borrow in the capital markets to pay for the deficits, funds that might otherwise go into the housing sector.

At a news conference on the task force report, Jay Janis, a former Federal Home Loan Bank Board chairman and former Housing and Urban Development undersecretary who served as a senior consultant on the task force, contended that lower mortgage rates won't by themselves close the "affordability gap." A major problem, he said, is the very cyclical nature of housing production, caused partly by seasonal factors and by the production and availability of raw materials and building supplies. But another factor is the federal government's reliance on monetary policy to control inflation, Janis said.

"When monetary policy is tight and interest rates are correspondingly high, housing demand slumps as home builders and the suppliers of such basic items as bath tubs and kitchen cabinets cut back on production," he said.

"But when interest rates drop, home buyers rush back into the market--putting tremendous demand pressures upon a home building and supply industry whose capacity is down," he explained. "Then we have the classic case of too much demand chasing too few goods, and housing costs heat up once again."

To alter the gloomy home ownership picture, the task force recommended that:

* Congress take steps to create more capital, including the establishment of tax incentives to encourage younger Americans to save. The group mentioned the possibility of an individual housing account, similar to the individual retirement accounts (IRAs), that could be used to channel money into housing.

* Changes be made to help home buyers compete for the capital that is available. The group recommended the creation of taxable bonds backed by federally insured deposits that would be attractive to pension fund managers and other institutional investors. The money attracted could be used to fund home mortgages.

* Local building and zoning code restrictions which unnecessarily raise the cost of housing be eliminated.

* The government end regulation of FHA and VA loan rates.

* The adjustable mortgage loan should be promoted as the standard instrument for financing home purchases.