How do you bolster the institution of marriage? Let homosexuals take part in it.

That's the argument of one gay-marriage (search) advocate, who says allowing homosexuals to marry instead of cohabiting or partnering in civil unions will create one "gold standard" of relationships. He says to do otherwise would weaken the institution of marriage by creating a menu of relationships.

"Same-sex marriage is the first attempt in many years to move back toward the expectation of marriage as a universal norm and the gold standard. With gay marriage, you say that marriage is for everybody," said Jonathan Rauch, author of the new book "Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America."

"When you get same-sex marriage, you eliminate the marriage-light alternative of civil unions (search) and partnerships. You send the signal that if you want the benefits of same-sex marriage, get married," he said.

But opponents argue that the same people who support allowing gay marriage are the very ones who oppose marriage as a basic building block of society.

Rauch's vision is part of "a dream world that isn't engaging the correlation of forces in society ... taking us in the direction of de-institutionalizing marriage in such a way that will put many more children at risk," said David Blankenhorn, founder and president of the Institute for American Values (search).

The gay-marriage debate emerged on the national scene in November, when the Massachusetts Supreme Judicial Court ruled that the state must permit gay couples to marry. In response, many socially conservative groups expressed worries that marriage will lose its meaning if gay couples are allowed to wed.

Feeling the pressure, President Bush expressed his support for a constitutional amendment banning gay marriage. He said it was for the "preservation of marriage."

"Ages of experience have taught humanity that the commitment of a husband and wife to love and to serve one another promotes the welfare of children and the stability of society. Marriage cannot be severed from its cultural, religious and natural roots without weakening the good influence of society," Bush said in February.

Marriage as an institution has already been subjected to serious challenges, primarily the increase in out-of-wedlock births and decreasing marriage rates, said Sarah Brown, director of the National Campaign to Prevent Teen Pregnancy (search).

One of the major traditional incentives for marriage — pregnancy — is no longer such a strong draw, with growing acceptance of births to unmarried couples as well as the easy availability of contraception and even abortion, she said.

"Marriage can be seen as an institutional response to the enduring power of the birds and the bees. Now sex need not lead to children. In short, the bedrock of marriage is eroding," Brown said.

But even with the obstacles, Brown said she was doubtful that gay marriage could get the institution back on track.

"It will take far more than gay marriage to bring order to the mess of marriage," she said. "There is no one way to fix it."

Rauch agreed that gay marriage will have only a marginal effect on the institution, but said it would be a positive one.

"Couples are detached from marriage. They increasingly see it as an option," Rauch said, adding that given the option, civil unions, the "halfway house between marriage and cohabitation," will end up becoming an attractive option to straight couples, further eroding the institution.

By not legalizing gay marriage, society "would validate cohabitation" and turn "every successful gay couple into a good example," he added. Marriage "will become one of many lifestyles; an item on a menu."

Blankenhorn conceded that heterosexuals are primarily responsible for weakening the institution of marriage, but he said gay marriage would detract further from the institution.

"If I thought, as Jonathan Rauch does, that gay marriage would turn the tide in a pro-marriage direction, I would wholeheartedly support that," he said.

Advising the nation to "proceed with caution" on the issue, University of Maryland professor Bill Galston predicted that the immediate effects of gay marriage would be positive.

"But the longer term effects are imponderable," he said. But Galston said he is hopeful.

"It is a cliché of our society that immigrants become the strongest patriots of our institutions. Might that not also be the case for marriage? Might gays also reinvigorate the institution that they're lining up to join? My hope is that this expansion of a long-cherished institution will have the same effect."

Blankenhorn said he too has hopes for marriage.

"My main hope for our country is that we can have more and more of our children growing up with two parents," Blankenhorn said.