Even though most Americans have grown more comfortable with same-sex or unmarried couples raising children, they still view single mothers as detrimental to society, according to a new poll of attitudes toward the country's soaring number of nontraditional families.

Most types of nontraditional families are broadly accepted or at least tolerated, including same-sex couples with children, unmarried parents and childless women, according to a poll by the Pew Research Center's Social and Demographic Trends. But two decades after TV's Murphy Brown caused a public furor by having a child without a husband around, many people continue to draw the line when it comes to single motherhood.

The poll illustrates how dramatically attitudes have changed from the not-so-distant past when the typical family was a married couple with children and virtually every other kind of family was considered abnormal. Today, nuclear families make up barely one in five households in the United States, Census Bureau statistics show. And nearly four in 10 births are to unmarried women, according to the National Center for Health Statistics.

"People aren't embracing these changes, but they are accepting them," said Rich Morin, a senior editor at the Pew Center and author of the report. "The days when people were made to wear a scarlet letter or were shunned after a divorce are ancient history."

The poll asked about 2,700 people for their views on seven trends in modern relationships that are upending what used to be considered the traditional family: unmarried parents raising children; gay couples raising children; single mothers; partners living together outside marriage; working mothers; interracial marriage; and women who never bear children.

The poll results suggest that Americans fall largely into three equally sized camps.

Roughly a third said the trends have no effect on society or are positive. People who had positive views of the changing family were overwhelmingly women, Hispanics and East Coast residents who rarely if ever attend religious services.

Another third considered most of the changes harmful to society. The only trends they accepted were interracial marriage and fewer women having children. They tended to be older, white Republicans who are married and religiously observant. They also were more likely to be from the Midwest or South.

The third group tended to accept all the changes except for single motherhood. Virtually all of them said the growing prevalence of mothers without male partners to help them raise children is bad for society. This group tended to be young, Democratic or independent, and more heavily minority.

Andrew Cherlin, a Johns Hopkins University sociologist who studies families, said the Pew poll underscores the widespread acceptance of two-parent families of almost any ilk.

"Working mothers are acceptable to almost everybody," he said. "Two parents who are unmarried are tolerated or acceptable. But many people, including single parents themselves, question single-parent families. There's still a strong belief that children need two parents."