Only the most affluent families in the United States will be able to own their houses if present housing trends continue, a study released yesterday by the Harvard-MIT Joint Center for Urban Studies says.

In 1970, almost half of all families in the U.S. could afford a median-priced house, but by 1975 only 27 per cent could afford a similar home.

Housing prices are rising so rapidly--almost doubling between 1970 and 1976--that the study's authors predict that an average home could cost $78,000 by the 1980s.

Bernard J. Frieden, professor of Urban Planning at MIT, who co-authored the study with Arthur P. Solomon, the center's director, said yesterday the center hopes its findings will serve as a warning to the government, which he said could reverse these trends by changing its housing policies.

In the past, the federal government has controlled the availability of mortgages, using them as a balance for the rest of the economy, rather than responding to housing needs, Frieden said.

However, he said, the first statements of Patricia R. Harris, Secretary of Housing and Urban Development (HUD) have sounded favorable to the kind of changes he would like to see.

A spokesman for HUD yesterday declined to comment on the study, which the department has not yet seen.

The study identifies increased sales prices, mortgages and interest payments, taxes and utilities as well as a record increase in the number of potential homeowners as major reasons for the rapid increase in homeowning costs.

Fragmentation

Both population pressure and a tendency among Americans to split up into smaller and more numerous housing units have increased demand for housing, and housing construction has not kept up with the demand, the study says.

"The old problem of people living in slum housing is gradually being eliminated," Frieden said. "What you have now is people living in better housing but paying a lot for it."

The government could alleviate this problem by giving lower and middle income groups help in paying for housing, he said.

The study also suggests that Americans are moving from metropolitan areas into smaller towns, and that there is increased migration to the south.

Frieden said the center has not examined the income brackets of the migrants, but he added that the move is not a flight to the suburbs by affluent city dwellers.

In fact, people are moving to smaller urban areas because they hope to find better employment opportunities, and because they have "itchy feet," he said.

For many families, the problem is not one of paying for housing but of poor community services, such as roads and schools, Frieden added.