NOSTALGIA and advertising have nourished an enduring image of the family as a cohesive unit in which the father is breadwinner, the mother is emotional caregiver, and all children are treated equally and well.
That such an image is largely a myth in the United States isn't a surprise. But the factors changing traditional family life here are taking their toll globally too, according to data compiled over the past two decades and described in a report released today by the New York-based Population Council.
The reality, says the report, is that mothers throughout the world have become important and sometimes primary breadwinners in the family, that fathers frequently cannot provide the economic and emotional support the family needs, and that children usually end up paying the highest price -- loss of the security and stability of a ''traditional'' family life.
''While families have always been characterized by change, there is strong evidence that they are changing faster than ever before,'' says the report, entitled ''Families in Focus.''
''... the present and future well-being of significant numbers of the world's children is in jeopardy because of adverse family circumstances.''
Cynthia Lloyd, one of the reports three principal authors, says, ''It has powerful implications at different levels, challenging false assumptions about family life on which governments have based economic and social policy and on which individuals have premised their futures.''
The report says five dominant trends are ''profoundly altering'' family life globally.
* Families and households are smaller.
* The average age of women at marriage and first childbirth has increased.
* Despite smaller family size, the burden of supporting dependents has grown heavier for working-age parents.
* The proportion of households headed by women has increased.
* Women's participation in the formal labor market has increased even as men's participation in the labor market has declined.
The report notes that families are under assault in rich and poor countries alike and often for the same reasons: rising divorce rates, the increased incidence of childbearing by unmarried women, and unstable employment.
Such problems are often exacerbated in developing nations by civil unrest or by the need for couples or fathers to migrate to find jobs or escape degraded environments.
The indices of family change are striking. One-third of all births in northern Europe are to unwed mothers, and between 20 and 30 percent in dozens of other countries. The number of households with dependent children headed by a single parent, meanwhile, has increased dramatically worldwide, now totaling one-quarter in the US, double the number 15 years ago.
As for marriages, 55 percent in the US now end in divorce. In Canada and several European nations, divorce rates more than doubled between 1970 and 1990.
According to the Council, after a divorce takes place the wife's income usually drops precipitously while the husband's drops only marginally.
Even so, husbands frequently shun child-support responsibilities, leaving mothers to bear virtually all the burdens of child-rearing in an era in which cash economies usually demand more than one salary can provide.
Absent the financial and emotional support of a father, children grow up in increasingly ''precarious and volatile conditions,'' the report notes.
Even if the mother remarries, it adds, children can get caught in a ''complex web of sibling relationships ... resulting in an uncertain claim on parents' attention and income.''
In most modern economies, motherhood extends beyond bearing and caring for children to providing for them financially, the report says. The problem is that opportunities to compete fairly in the marketplace are often lacking, thanks to laws and customs that bar women from holding title to land, for example, or gaining access to credit.
For families to survive and stay out of poverty, the report concludes, mothers will have to add income-generating work to their child-care responsibilities, even as men add child-care responsibilities to their work.
Governments will also need to recognize the changing nature of families, adopt policies to ease the burden on mothers and prompt fathers to contribute more to the family.
Family-life education is also needed to prepare girls for the likelihood that they will have to run a household alone and boys for the responsibilities of eventual parenthood, says the Council.
''The parent-child relationship is the fundamental building block of human society; if it is broken under the assault of misguided policies, little else will be left to lose,'' it concludes.