Americans today are choosing more often to live in traditional household groups than they did in the 1970s, reversing the trend of singles, mingles and divorced people setting up housekeeping by themselves that dominated the last decade.

Kenneth Rosen, chairman of the real estate and urban economics program at the University of California at Berkeley, said that although traditional married couples accounted for only one-quarter of the new households formed in the '70s, the traditional "station-wagon, home in the suburb" family is expected to account for at least half of new households formed in the 1980s, double the rate in the '70s.

Housing economists say, however, that it is still unclear whether this new trend is a reflection of a return to more traditional values and life styles or merely a function of the increasing cost of housing. And some believe that it could be simply a reflection of the uneven population distribution among age groups.

Gopal Ahluwalia, an economist with the National Association of Home Builders, attributes the changing trend to a combination of factors, including the fact that the Baby Boom generation (people born between 1946 and 1964) is beginning to approach middle age and is increasingly adopting more traditional living arrangements than it did in the '70s.

He said that at the same time, the Baby Bust generation (born between 1965 and 1975) is beginning to graduate from high school, the period when people traditionally have tended to set up single-person households. This group, however, is much smaller in number than the Boomer generation and is finding that the rising cost of housing and rentals makes moving away from home less attractive than it was for their older siblings.

"You can only leave your parents or spouse if you can afford alternative housing," said George Sternlieb, director of the center for policy research at Rutgers University. "The capacity of people to leave each other is a function of the capacity to afford housing, and we have seen a precipitous decline in the capacity to afford housing among Americans over the past several years."

Sternlieb said that his research shows that of the 20 million housing units added to the U.S. housing stock in the decade of the '70s, roughly half were built to accommodate fragmenting households rather than population growth.

"What we have seen in the past four years, however, is a reverse. There are a lot of young people coming back to live with their parents when they find they can't afford to set up house by themselves, or unhappy married couples choosing to stay together because they cannot afford to live separately."

Alfred Gobar, a market economist who analyzes housing markets in 130 U.S. cities, said that he started seeing a noticeable increase in the percentage of larger households staying together as early as 1976, and that it first showed up and continues to be strong in cities with high-cost housing.

Sternlieb said that an average of 1.7 million new households were formed each year during the '70s, but that for the first four years of the '80s the average annual household formation was only 1.3 million, even though the "best demographers in the country" predicted household formation in the '80s would run higher than in the previous decade. Ahluwalia said that for the '90s that figure is expected to drop further, to only 1.2 million a year.

"Housing in the United States used to be very cheap, and while that began to change in the '70s, inflation covered over the real cost for a while," said Sternlieb. "The real impact of the increase wasn't felt until the recession hit, inflation fell and interest rates stayed high. The big question for the housing industry now is whether we will see a return to smaller households as the economy continues to recover."

Steve Rawlings, a family demographer with the family statistics section of the Census Bureau, said that he also has seen a drop in the rate of household formation by unmarried adults and single adults with at least one dependent, though he said that in actual numbers, these households still are increasing.

He said, however, that a large increase in the rate of new households formed by single women with at least one dependent partially offset this trend.

Rawlings said that as of March 1984, there were 85.1 million households in the United States. Of those, 50.1 million were married couples, 23.4 million were singles living alone, 9.9 million were single women with at least one dependent, and 2 million were single men with at least one dependent. Of the roughly 50 million married couples, roughly half had at least one child under 18 years old.

Ahluwalia said that other factors also have affected the rate at which Americans are forming more traditional households. He said that the divorce rate fell last year for the first time in 15 years, and that the Baby Boomers' tendency in the 1970s to delay marriage accounted for the surge in marriages in the early '80s.

"Whether the decreasing divorce trends are here to stay is unclear," said Ahluwalia, but the pattern of delaying marriage shows "little sign of declining."

Rosen said that this year he has seen a surge in the number of single-person households being formed, but believes it is a "one-time" event, attributable to the recovering economy.

"I believe it is a one-time shot because most of it was probably a result of demand pent up during the recession," said Rosen. "Single household formation is most sensitive to a recession because single people have a harder time affording their own place than a couple."

Some local builders and Realtors say they have seen signs of the turn to more traditional households, but that it is not as extreme in Washington as it appears to be nationally.

Mike Was, director of marketing for Reston Land Corp., said that in a 1983 survey of people looking for houses in Reston, potential home buyers last year had a higher percentage of married couples than the 1982 group. They also tended to have more children, and a higher percentage were two-income families, an indication that it is taking more income for the average family to buy a house than it used to.

James M. Merrion, president of local residential real estate services for Coldwell Banker, said that in the Washington area he has seen less decline in the number of single people willing to invest in housing with an unrelated friend.

"It may be true on a national basis that there are more couples forming households than singles, and I have seen evidence of that trend and a return to more traditional values in other U.S. cities, but around here it is less true," said Merrion. "Singles here are well-educated, professional people who see that this housing market has a history of being dynamic, and many of them are getting into sharing equity with a friend if they are not married so they can take advantage of the market."