Financial institutions, already hard pressed to meet mortgage lending need, will continue to see savings deposits decline and with them the prospects for future homeownership as the demand for home financing increase, housing industry economists are predicting.

The only hope of reversing this trend, say the economics, lies in the adoption of policies that encourage saving and attract money to housing from such nontraditional sources as pension funds, insurance companies and private investors, including consumers, who could be allowed to invest in mortgagebacked securities at their local savings institutions.

If these changes do not occur, the economists agree, mortgages will be difficult to obtain and interest rates will not drop significantly during the 1980s.

As the number of families in the first-time home-buying age increases during the remainder of this decade, many who bought homes since 1979 using short-term creative financing arrangements will be approaching lenders for long-term refinancing. Thus, lenders will be asked to fund both current and past buyers, the economists note.

Nationally, more than a million home sales have been financed with short-term loans in the last three years, according to economist Kenneth Kerin of the National Association of Realtors.

"The major chunk of creative financing will be coming due starting later this year and continue for another four or five years," points out James Christian, chief economist of the U.S. League of Savings Associations. "When this happens, we will be facing a major problem."

"This is a problem we've never experienced before," said Thomas R. Harter, senior staff vice president and chief economist of the Mortgage Bankers Association. "Creative financing amounts to borrowing against the future. Because of creative financing there will be tremendous demand for mortgage credit without a single transaction occurring."

At the same time, the size of the 45 to 65-year old age group, which is the prime saving group, will be decreasing, economists further point out.

In 1987 we'll reach the worst demographics for saving i the entire last half of the 20th century," said the U.S. League's Christian. "We're liable to show negative personal savings."

Changes in the operations of financial institutions will accelerate the fund shortage, economists add. Savings and loan associations and savings books will continue to compete with money market funds and other programs for funds and will operate in nationwide competitive markets, rather than in local real estate markets. Thus, while the source of their funds will provide less money, demands for their funds will expand.

"Local borrowers are competing for credit with borrowers in other regions of the country, with major corporations both here and abroad, with the U.S. government and even foreign governments," stated a recent report, Homeownership: The American Dream Adrift, by the U.S. League's economics department.

"The born-again thrift," predicts economist Mark J. Riedy, the MBA's executive vice president, "will operate nationwide, both seeking and investing its funds at highly competitive capital market rates. Indeed, it is the transition from localized, protected savings and mortgage markets to nationwide, fully competitive markets that lies at the heart of the transition problems in the real estate finance industry."

Demanding for financing from what could be a shrinking pool of savings will come from the commercial world as well as the consumer world, economists say to explain another aspect of the home financing problem. Christian says that even if savings and loan associations and other thrift institutions maintain their traditional level of investment in real estate, the mix probably will change, with a smaller proportion going to homes.

Each home loan that lenders do make will require more money because of rising home prices, Christian adds. Add he notes that the baby-boom generation that is expected to push the demand for housing to two million homes a year will also need financing for other items.

They'll be buying washers and autos as well as homes," he points out.

Both Christian and Riedy also point to a declining inclination to save.

"The supply of consumer savings from disposable income has diminished as a share of income as a result in the last decade," said Riedy, who was vice president and chief economist of the Federal Home Loan Bank of San Francisco before joining the MBA in 1973. "Moreover, because of increased financial sophistication on the part of consumer and the growing inability of thrifts, in particular, to compete effectively for those savings, mortgage credit has become less readily available and increasingly expensive over time."

Christian estimates that the savings rate at S&Ls and banks (as a percent of disposable income), which averaged 7.1 percent in the 1970s, will drop to between 5.7 and 4 percent in the 1980s possible going as low as 2 percent if umemployment drops to 5 percent. It was in the 4 percent range at the end of the 70s but is higher today it was 6.6 percent for the first half of '82, and is expected to lower to 5.7 percent for 1983.

The U.S. League's economics department report says that these changes in saving behavior "compound the capital shortage suggested by the change in demographics.

"Easier access to credit through credit cards, charge accounts and other forms of consumer credit has reduced the need to keep money in checking accounts and to save up for major purchases," it states. "The spread of corporate group health, accident and life insurance, along with government programs such as Medicare, Medicaid, unemployment and disability insurance programs has reduced the felt need of households to save for rainy days."

The gap between mortgage demands and available money could reach $226 billion by 1990, accourding to a recent study by the University. Similarly, a recent forecast by the American Bankers Association says that savings and loan associations and savings banks "will probably be unable to fulfill much more than a third of mortgage credit demand" by 1990.

"Even if inflation rates are held to single digits," concludes Christian "mortgage interest rates in the 1980 would be significantly higher than they were in the '70s."