Can Warren Buffett and Bill Gates save the world?

Twenty-five years ago, when Steve Hilton was an entry-level guy working in the file room at his family's foundation, he sometimes had to explain his place within the family legacy.

His grandfather Conrad, the son of an immigrant shopkeeper, turned a single 40-room hotel in Cisco, Texas, into an international empire – the ur -American tale of self-made wealth. His father, Barron, expanded the family business even more, eventually selling the hotel conglomerate in 2007.

But both these Hiltons gave away the vast majority of their fortunes, putting their billions into a charitable trust charged to "relieve the suffering, the distressed, and the destitute."

"When I first started, and people said, 'What do you do?' I would say, 'Well, I work for a foundation,' " says the younger Mr. Hilton, now the president and chief executive officer of the Conrad N. Hilton Foundation, the 25th largest charitable trust in the world. "And they would say, 'Oh, you're in construction?' I'd say, 'No, we give money to charitable groups.' And then there'd be a long pause. Then they'd say, 'You don't do that full time do you?' "

Today, however, from icons of pop culture to titans of American business, the act of giving away money, even in staggering sums, is gaining a new cultural momentum. Call it a new form of noblesse oblige, complete with modern media hype and celebrity cachet: It's the rich and the famous now who lead the entreaties to give.

But even the well-publicized efforts of superstars like Bono and Angelina Jolie cannot compare with the potentially globe-changing quest of Warren Buffett and Bill Gates, the two richest men in America. For over a year now, in a new voluntary, ad-hoc association called the Giving Pledge, these self-made mega-billionaires have been urging their peers to donate at least half their fortunes for the common good.

They are asking the über-rich in America – as well as around the world – to stand up publicly and commit hundreds of millions, if not tens of billions, of dollars to the charities of their choice. The Giving Pledge, they say, is neither an effort to pool resources nor a call to raise funds for a cause. It is simply a moral commitment to give.

"With wealth comes responsibility to help make the world a better place," says media mogul Ted Turner in an e-mail from Nigeria, where he is surveying efforts to fight disease. "I believe anyone who is fortunate enough to achieve financial success has a moral obligation to use that money for the greater good. America is the world's most generous nation on both a government and individual level. But I believe that we have not yet lived up to our responsibility and can kick it up a notch."

At the same time, however, these efforts may represent a particularly American vision of the common good – one that includes proclaiming a cause with all the moral fervor of an evangelist. It's a vision that highlights stark differences between this country and much of the rest of the world.

"We're hoping that America, which is already the most generous society on earth, becomes even more generous over time," said Mr. Buffett in a conference call with reporters in August. "And the norm in this society, probably kicked off to a significant extent by Rockefeller and Carnegie, has moved toward more generosity, up and down, by the rich, the poor, and the in between."

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