WASHINGTON - A record number of American women are now the sole or primary breadwinners in their families, a sign of the rising influence of working mothers, a new study finds. Mothers now keep finances afloat in 40 percent of households with children, up from just 11 percent in 1960.

While most of these families are headed by single mothers, a growing number are married mothers who bring in more income than their husbands, according to a study released Wednesday by the Pew Research Center.

As the numbers have shifted, however, public attitudes have remained mixed regarding the impact of working mothers on families. People are not at all sure it's a good thing.

Demographers say the change is all but irreversible and is likely to bring added attention to child-care policies as well as government safety nets for vulnerable families.

"This change is just another milestone in the dramatic transformation we have seen in family structure and family dynamics over the past 50 years or so," said Kim Parker, associate director with the Pew Social and Demographic Trends Project.

The trend is being driven mostly by long-term demographic changes, including higher rates of education and labor force participation dating back to the 1960s women's movement. Today, women are more likely than men to hold bachelor's degrees, and they make up nearly half - 47 percent - of the American workforce.

But recent changes in the economy, too, have played a part. Big job losses in manufacturing and construction, fields that used to provide high pay to a mostly male workforce, have lifted the relative earnings of married women.

At the same time, marriage rates have fallen to record lows. Forty percent of births now occur out of wedlock, leading to a rise in single-mother households. Many of these mothers are low-income with low education, and more likely to be black or Hispanic.

Andrew Cherlin, a professor of sociology and public policy at Johns Hopkins University, predicts the growing numbers will lead to a growing constituency among women in favor of family-friendly work policies such as paid family leave, and safety-net policies such as food stamps or child-care support for single mothers.