Less than a week after Hurricane Katrina, American giving to help storm victims has surged past the level raised for South Asia tsunami relief in the same period, nearing the $100 million mark, according to charities and experts. But relief groups and federal officials worked to keep the donations flowing from Americans worried about oil prices and the economy.

President Bush yesterday appointed his father, former president George H.W. Bush, and former president Bill Clinton to spearhead fundraising for hurricane victims, in a reprise of their roles as tsunami money-raisers earlier this year. The American Red Cross, which has raised three-quarters of the total, planned a national direct-mail appeal as it welcomed a $5 million donation from Texas energy baron T. Boone Pickens. Corporations gave one-third of the total so far: Wal-Mart Stores Inc., the nation's largest retailer, has pledged $17 million to the relief effort, the largest corporate donation yet, with chief executive H. Lee Scott Jr. delivering the commitment by phone to Clinton, officials said.

Charitable organizations across the country said that while the windfall was beyond anything they had experienced, it represents only a fraction of what will be needed for a rebuilding effort expected to last years.

"This is going to be the most massive need we've seen in our history," said Maj. Dalton Cunningham, the Salvation Army's divisional commander for Alabama, Louisiana and Mississippi. "But the challenge comes when the emotionalism of the event dies."

Over the past 24 hours, pledges to hurricane relief charities quadrupled, to nearly $95 million late yesterday, according to the Chronicle on Philanthropy, a publication that tracks charitable donations. The Red Cross accounted for more than $72 million of that total. Contributions to the Salvation Army's hurricane fund swelled to more than $15 million, powered by individual contributions ranging from $10 to a check for $38,000 from an anonymous walk-in donor in Mississippi.

Internet donations accounted for nearly one-third of the total raised so far, roughly the same as in the tsunami aftermath, according to Chronicle on Philanthropy figures. That is more than twice the proportion of online gifts made in the aftermath of the Sept. 11, 2001, terrorist attacks. In peak hours over the past two days, Network for Good, an online contribution site based in Vienna, Va., that channels contributions to a host of charities, was processing 1,800 hurricane relief gifts an hour, or one every other second.

But leaner days may be ahead. "I think the fact that gas prices are going up and there's overall concern about the health of the economy could be a long-term stumbling block" for charities, said Stacy Palmer, editor of the Chronicle of Philanthropy.

According to Indiana University's Center on Philanthropy, downturns in the stock market and personal income levels are two of the best predictors of a fall in charitable contributions.

The challenge for charities, said Patrick Rooney, the center's director of research, will be emphasizing not only the severity but also the scope of the destruction. "That's one of the reasons tsunami relief was so generous," he said. "People realized this was not just a matter of short-term emergency relief but of long-term, structural rebuilding of whole societies."

Staff writer Michael Barbaro contributed to this report.

President Bush appoints former presidents Bill Clinton and George H.W. Bush to spearhead fundraising for victims of Hurricane Katrina, in a reprise of their roles heading the drive for victims of last winter's Asian tsunami. Meanwhile, the Senate passed Bush's request for $10.5 billion as a down payment on federal storm relief. Story, Page A17.

Fresh water reaches two young Hurricane Katrina survivors in New Orleans.