The individuals, whose combined income accounts for more than 1% of all the money earned by 292 million Americans, provided nearly 7% of all gifts in 2000, the year to which the figures relate.
While the names of the 400 are not given, they are believed to include Bill Gates, George Soros and Ted Turner, all of whom are known to have given huge amounts. But the charitable group which paid for the information to be collated, NewTithing Group, believes they could all give a lot more.
Claude Rosenberg, the retired money manager who founded the organisation, told the New York Times the top taxpayers could have afforded 40% more.
Research shows that donations from the very wealthy have continued to decline when measured against their assets, and relatively little has directly benefited the poor.
Meanwhile, the US government has cut taxes for the wealthy and benefits for the poor, while making charitable donations tax-deductible.
"For an organisation to qualify as charitable doesn't mean it benefits the poor," said Lewis Feldstein, president of the New Hampshire Charitable Foundation. "[Institutions] that benefit tend to be connected to people of means, like land charities, museums, colleges and hospitals."
Nonetheless, between 1997 and 2000 the growth in their charitable donations outpaced the rise in their incomes; incomes rose 80% while giving went up by more than 400%.