The American dream of home ownership is in danger of becoming obsolete within half a decade because by then the average house will cost $78,000.

That is the major finding of an authoritative study of the nation's housing plight conducted by Massachusetts Institute of Technology and Harvard University.

Already, according to the Harvard-MIT, Joint Center for Urban Studies, the sale prices of new houses have increased twice as fast as family incomes; barely a quarter of the nation's house holds can now afford a home costing $48,200, the current average price.

The poorer third of the population has been completely priced out of the market, and the only families who can afford to own the average house are earning $20,000 or more - the top quarter of the nation in terms of earning power.

The price spiral will escalate above $78,000 for modest new homes beyond the 1980s, and most of the middle-class population will be hard-pressed to own their own homes, the study said.

"We're not crying out a crisis, but we do have the warning signs of a crisis a few years down the road," said Arthur P. Solomon, director of the joint center and a former White House adviser to President Johnson.

The Harvard-MIT research organization has been preeminent in forecasting housing needs since its widely publicized 1973 study disclosed that 13 million American homes were physically unsound, overcrowded or excessively expensive for the occupants.

Since 1970, according to the study realised here today, the average-income family has lost ground as the [WORD ILLEGIBLE] of home ownership - mortgage and interest payments, taxes, insurance and maintenance - has outstripped increases in income.

The median sales price for new homes increased nearly 90 per cent from 1970 to 1976, and the monthly ownership costs of new homes increased during the same period by more than 100 per cent.

The median sales price for existing homes increased 65 per cent in the same period, and the monthly ownership costs for existing homes jumped 73 per cent.

In contrast, the median income, nationally, increased during the period by 47 per cent, while the consumer price index rose 48 per cent.

"The cost squeeze on middle-income families is replacing the slum as the major problem in housing in this country," said Bernard Friedman, coauthor of the report, which was funded in part by the Department of Housing and Urban Development.

The study disclosed that:

Despite a near-record 1.6 million new housing starts in 1976, the number is 20 per cent below current need.

While in 1970 almost half the U.S. families could afford to buy average-priced nw homes, only 27 per cent of the families could afford an average-priced new home last year.

The number of low-income families living in physically inadequate units has declined since 1960, but the number paying an unreasonably high percentage of their incomes on housing has more than doubled.

While the commonly accepted measure for personal finance used to allow for one-fourth of monthly salary for housing costs, many U.S. families are now paying 35 per cent or more.

To compensate for spiraling house costs, the research team found, Americans are making concessions that significantly affect their quality of life. Some withdraw from the housing market and become renters, while others resort to pooling the incomes of both husband and wife.

Other families stretch their resources thinly by eliminating many nonessential expenses, while some have resorted to buying mobile homes.

At the same time, thre are sociological factors increasing the pressure on the housing market, the study found. These include increasing numbers of young adults and senior citizens who split from the family nucleus to set up housekeeping, and a steadily increasing divorce rate.

Also, population shifts toward the Sun Belt states and the exurbanareas of the Northcentral and Northeast regions of the country are creating additional housing pressures in some area.

The Harvard-MIT unit called for a "strong national housing policy with a constructive partnership between the public and private sectors."

The policy, the group reported, should focus on better and more affordable housing for the poor, with secondary emphasis on improving the home-buying climate for the young and persons with average incomes.

When pressed for specific recommendations, Solomon and Friedman suggested reforms in federal monetary policies that would lower the home mortgage interest rate, possible adoption of a variable mortgage interest rate that would fluctuate with rises and drops in inflation, re-examination of environmental restrints on the housing industry that push home development costs upward, and adoption of new regulations that would help stabilize the cyclical effects of the roller-coaster construction industry.