Social science overwhelmingly supports the idea that marriage is a valuable institution.

Compared with other groups, married men and women are more likely to be wealthy and healthy, live longer lives, and have high levels of sexual satisfaction and low levels of depression and suicide, Linda J. Waite and Maggie Gallagher wrote in "The Case for Marriage: Why Married People are Happier, Healthier and Better Off Financially," which was published in 2000.

Marriage especially benefits children: Those in married-parent homes are at low risk for living in poverty or suffering neglect or abuse, the women wrote. They are more likely to do well in school and avoid risky behaviors, such as premature sexual activity and drug and alcohol abuse.

Growing up with successfully married parents provides children with a home in which security, trust, safety, problem-solving skills and, typically, a spiritual life are present, the women wrote. Married-couple families also bind extended families, creating "clear ties of begetting and belonging, ties of identity, kinship and mutual interdependence and responsibility," about 70 scholars wrote in a paper released in July by the Witherspoon Institute in Princeton, N.J., on how marriage is linked to "the public good."

Marriage and family even stand as pillars in a free society, historian Allan Carlson wrote in his new book, "Conjugal America: On the Public Purposes of Marriage." "The first target of any totalitarian regime is marriage," he wrote, citing examples from Soviet and Chinese communist regimes and Germany under Nazism.

Much has been written about the changing characteristics of American families -- notably, the slow decline of marriage rates and the increase in unmarried cohabitation, single-person households and unwed birthrates.

"Americans have become less likely to marry," concluded the 2006 State of Our Unions report, written by National Marriage Project (NMP) co-directors Barbara Dafoe Whitehead and David Popenoe.

Researchers have attributed the enormous changes in America's family formation to the introduction of the birth-control pill, which permitted sex without pregnancy; the en masse entry of women into the work force; and the growing belief that couples should postpone marriage until they get a college degree, a steady job or a mortgage -- preferably all three -- even if it takes until they are almost 30.

Another factor is the relatively modern idea that people should marry "for love," said history professor and author Stephanie Coontz. When marriage changed from a "mandatory economic and political institution" into a "voluntary love relationship," it became more flexible -- and more optional, said Mrs. Coontz, director of public education at the Council on Contemporary Families. "Trying to revert to antiquated and unfair traditions is not the answer," she said. "We need to figure out how to build on the opportunities and minimize the risks associated with the ongoing modernization of marriage."

Mrs. Whitehead and Mr. Carlson see other factors at work, including the belief that marriage is first and foremost a personal relationship for adults.

Having children often is viewed as a disruption in one's life course rather than a defining purpose, Mrs. Whitehead wrote in an essay accompanying the NMP's report.

The "most satisfying" adult years are those "before children" and "after children," while the child-rearing years are the "bone-wearying and time-consuming work" that cuts into time that could have been better spent, she writes.

The 24/7 work culture quietly reinforces these perceptions. Married parents are tied down and tired, while childless adults and couples not only have energy but the freedom to pick up and move, work odd hours and go on the road. The marketplace, too, likes dual-income couples with no children because they have both the inclination and the income to dine out, take vacations, buy big-screen TVs, join health clubs, go to sporting events and enjoy $4 cups of coffee.

In contrast, raising children is viewed as a budget-buster: The U.S. Department of Agriculture has estimated that it costs $237,000 to raise one child to adulthood.

On top of this, child-rearing means years of high anxiety and even psychological shock to adults -- especially educated, professional women who are accustomed to spending their time in ways that are personally satisfying, intellectually fulfilling and socially independent, Mrs. Whitehead wrote.

"Motherhood is an abrupt departure from this pattern" in that it monopolizes time and requires outstanding performance but offers none of the "workplace" perks. "No one gives [mothers] a bonus or even a pat on the back for sitting up all night with a sick child or playing peek-a-boo and patty-cake with toddlers all day," she added.

"What's more," Mrs. Whitehead wrote, "contemporary motherhood now threatens contemporary marriage." Most Americans marry for love, friendship and emotional intimacy, a goal that requires high levels of time and attention, she wrote.

"The problem is that once a real baby comes along, the time, the effort and energy that goes into nurturing the relationship goes into nurturing the infant. As a result, marriages can become less happy and satisfying during the child-rearing years."

Mr. Carlson takes these views even further, calling the bond between marriage and procreation the "social and moral foundation of Western Christian civilization."

Early Christian fathers favored procreative marriage to encourage sexual fidelity and the divine blessings of children, Mr. Carlson wrote in "Conjugal America."

Eventually, especially in America, he added, loving married couples and big families became an ideal so obvious that the French observer Alexis de Tocqueville noticed it. "There is certainly no country in the world where the tie of marriage is more respected than in America, or where conjugal happiness is more highly or worthily appreciated," de Tocqueville said after visiting here in the late 1820s.

However, America is moving away from the view that marriage is a public good and the nation must have an abundance of "functional, child-rich homes" to thrive, says Mr. Carlson, president of the Howard Center for Family, Religion and Society.

Family policy "should not try to re-create the framework of 50 years before. It must do better," he says. But "new protections and encouragements to marriage are now imperative."

In the marriage arena, two forces for change have been particularly notable. One is a "marriage movement," formed six years ago to reverse the trend of family breakdown in America.

Current domestic policies "are based on acceptance of family breakdown and are focused on dealing with the aftermath and fallout," Diane Sollee, director of the Coalition for Marriage, Family and Couples Education, said when the group's "statement of principles" was announced in June 2000.

The original statement -- signed by more than 100 academic, religious, political and civic leaders -- was updated in 2004, with 86 pledges for action, including expanding marriage education, reforming state divorce laws and developing model pro-marriage legislation.

Pro-marriage allies also received an unprecedented boost this year when 225 pro-marriage and responsible-fatherhood organizations were awarded federal grants worth nearly $120 million a year.

The new five-year funding "shows where our priorities are," says Elizabeth Marquardt, author of "Between Two Worlds: The Inner Lives of Children of Divorce" and director of the Center for Marriage and Families at the Institute for American Values.

It also revealed an important political consensus -- that both Republicans and Democrats think marriage matters, she says. Such a consensus "is a significant achievement" that should bring long-term dividends, beyond the marriage grants.

When the debate over homosexuals' right to "marry" emerged in the early 1990s, traditional-values groups were tongue-tied in their defense of marriage. How could anyone question the value of such a bedrock institution, they thought -- until the Hawaii Supreme Court ruled in 1993 that restricting marriage to bride-and-groom couples illegally discriminated against same-sex couples.

Today -- especially now that 28 states have held public votes on constitutional amendments to define marriage as the union of one man and one woman -- homosexual rights groups and traditional-values groups have honed their arguments and Americans have been repeatedly forced to think about the definition, purpose and value of marriage.

"I think the same-sex marriage debate has wakened us up," Mr. Carlson said. "For 40 years, American policy-makers and American citizens have allowed marriage law and marriage policy to drift into some terrible problems.

"We've gone from being the 'marryingest' people" in the world to the nation with one of the highest, if not the highest, divorce rate, "and that's not a healthy change." Of course, all the talk about the definition, purpose and value of marriage has sparked some proposals that were unthinkable to most people a few years ago.

In August, for instance, about 270 homosexual activists and their allies issued a statement about why legalizing same-sex "marriage" doesn't go far enough. Because marriage is "not the only worthy form of family or relationship," it "should not be legally or economically privileged above others," said the statement titled, "Beyond Same-Sex Marriage: A New Strategic Vision for All Our Families and Relationships."

The "challenge that lies before us as a nation is how to support all relationships and families, not just married ones," says the Alternatives to Marriage Project, which calls for an end to "discrimination on the basis of marital status" in its family-diversity statement.

A new voice entered the marriage debate this summer when the Witherspoon Institute issued a paper, "Marriage and the Public Good: Ten Principles."

"As scholars, we are persuaded that the case for marriage can be made and won at the level of reason," said the 70 scholars of history, economics, psychiatry, law, sociology and philosophy who signed the principles.

The paper lists divorce, non-marital childbearing, cohabiting and same-sex "marriage" as threats to marriage -- the latter because "it would create a new way of looking at marriage," says Luis Tellez, president of the board of trustees for the Witherspoon Institute.

"If we institutionalize marriage between just anybody, it won't stop there ... the next question will be polygamy," he says. And while polygamy has a long history and still exists today, "the great majority of societies" settled on monogamous one-man, one-woman marriage as they became more civilized, he says.

Meanwhile, say the scholars -- including Robert P. George of Princeton University, Mary Ann Glendon of Harvard Law School and Jean Bethke Elshtain of the University of Chicago -- the "great goal" is for more children each year to be "raised by their own mother and father in loving, lasting marital unions."

"The future of the American experiment depends on it. And our children deserve nothing less," they say.

Cheryl Wetzstein is National Reporter for The Washington Times