Nearly half of American dads under 45 this Father's Day say they have at least one kid who was born out of wedlock. And the share of fathers living apart from children is more than double what it was not so long ago.

In encouraging news, though, among married fathers, children are said to be getting more attention from both parents at home than ever before.

A Pew Research Center report highlights the changing roles of parents as U.S. marriage rates and traditional family households fall to historic lows.

For example, college-educated men who tend to marry and get better jobs are more involved with their children than lesser-skilled men struggling to get by.

"When a father can't provide monetarily for his offspring, he often becomes estranged," said Beth Latshaw, an assistant sociology professor at Appalachian State University, who researches changing paternal roles. She pointed to an economic advantage for college graduates hired at companies with better benefits and family-friendly policies, contrasted with the situation for the larger ranks of low-wage workers.

"As a result, many women now raise children outside of marriage or without a father figure," Latshaw said.

Pew's survey and analysis of government data, released Wednesday, found that more than one in four fathers _ or 27 percent _ with kids 18 or younger live away from at least one of their children. That number is more than double the share of fathers who lived apart from their kids in 1960.

On the other hand, married fathers who live with their children are devoting more time helping their wives with caregiving at home, a task once seen almost exclusively as a woman's duty. Such fathers on average now spend about 6.5 hours a week on child care, which include playing, helping kids with homework or taking them to activities. That's up from 2.6 hours in the 1960s.

The 6.5 hours is still just half the amount of time mothers spend per week. Still, it is a gap that is narrowing; in the 1960s, fathers put in one-fourth the time mothers did.

"Father's Day reminds us parents that we have no more solemn obligation than to care for our children. But far too many young people in America grow up without their dads, and our families and communities are challenged as a result," President Barack Obama said Wednesday in calling for fathers to be more involved. Next Sunday is Father's Day.

Obama has often reminded Americans how his father left his family when the future president was a small child, describing a "hole in a child's life that no government can fill." The Health and Human Services Department in conjunction with the Ad Council is now running public service advertisements this week urging fathers to "Take Time to Be a Dad Today," and the administration next week is expected to announce new support for local fatherhood programs.

The ads this year focus on Hispanic fathers and military dads sharing small moments with their children.

The Pew study, entitled "A Tale of Two Fathers," found sharp differences based on race and education. Black and Hispanic fathers were much more likely to have children out of wedlock, at 72 percent and 59 percent, respectively, compared to 37 percent for white men. Among fathers with at least a bachelor's degree, only 13 percent had children outside marriage, compared to 51 percent of those with high school diplomas and 65 percent of those who didn't finish high school.

Age, too, was a factor. Three-fourths of fathers who were 20 to 24 had children out of wedlock, compared to 36 percent for fathers 35 to 44.

The findings come as the latest census data show that marriages have fallen to a record low, pushing the share of U.S. households with married couples below 50 percent for the first time. Sociologists say younger people are increasingly choosing to live together but delay marriage as they struggle to find work and resist making long-term commitments.

Gretchen Livingston, a senior Pew researcher who co-authored the report, noted that fathers who live away from their children are not always absent from their kids' lives. More than 20 percent of such dads said they saw their children several times a week, and even more _ 41 percent _ kept in touch regularly through phone calls or email.

Still, 27 percent of fathers who live away from their children reported that they didn't see them at all in the past year, and almost one-third communicated by phone or email with their children less than once a month.

"Overall, we can't say whether kids are better off or not," she said.

Other findings:

_In all, about 46 percent of fathers ages 15 to 44 say they had at least one of their children born outside of marriage. That figure tracks closely with government data showing the share of babies born to unwed mothers jumping eightfold, from 5 percent in 1960 to 41 percent in 2008.

_The public is divided over whether fathers are more involved in their children's lives than 20 or 30 years ago. About 46 percent say dads today play a bigger role, while 45 percent say they are less involved.

_Despite greater involvement of some married fathers, the number of hours mothers spent per week taking care of children at home rose modestly from 10.6 hours in 1965 to 12.9 hours in 2000. Some sociologists say that may be due to fathers seeing themselves as secondary caregivers, more apt to play with children while the mothers change diapers or manage schedules.

_Among all adults, 57 percent say it is more difficult to be a father today than it was 20 or 30 years ago. About 9 percent say being a father is now easier, while 32 percent say it is about the same.

Pew based its findings on Census Bureau figures as well as National Center for Health Statistics survey data from 2006-2008, the latest available. On behalf of Pew, Princeton Survey Research Associates International also interviewed 2,006 people 18 and older by cellphone or landline from May 26-29 and June 2-5. The Pew survey has a margin of error of plus or minus 2.6 percentage points.

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Online:

Pew Social and Demographic Trends: http://pewsocialtrends.org