New York ? The numbers are almost too large to fathom, so many Americans stop trying. As bodies pile up in disaster after global disaster, even the most sympathetic souls can turn away.

Charities know this as “donor fatigue,” but it might be more accurately described as disaster fatigue – the sense that these events are never-ending, uncontrollable and overwhelming. Experts say it is one reason Americans have contributed relatively little so far to victims of the Myanmar cyclone and China’s earthquake.

Ironically, the more bad news there is, the less likely people may be to give.

“Hearing about too many disasters makes some people not give at all, when they would have if it had been just one disaster,” says Michal Ann Strahilevitz, who teaches marketing at Golden Gate University and specializes in the factors at play in charitable giving.

Compared with disasters like the Asian tsunami and Hurricane Katrina, those in China and Myanmar have generated just a trickle of aid. As of Friday, Americans had given about $12.1 million to charities for Myanmar, according to the Center on Philanthropy at Indiana University. The group said on Monday that it was too soon to count contributions to China.

A number of factors may be at play in the slow American response, including a lack of sympathy for the repressive governments involved, doubts about whether aid will get through, and an inclination to save pennies because of shaky economic times at home.

But Americans may have also been influenced by the quick succession of monumental catastrophes in two distant lands. At least 130,000 people are dead or missing in the Myanmar cyclone, and more than 40,000 confirmed deaths in China’s earthquake.

The 2004 Asian tsunami brought $1.92 billion in charity from the United States, according to the Giving USA Foundation. Hurricane Katrina eight months later generated even more, $5.3 billion.

But then fatigue seemed to set in. The earthquake in Pakistan that killed nearly 80,000 people generated just $150 million from Americans. The Guatemala mudslide shortly thereafter that killed at least 800 was virtually forgotten.

It’s too soon to judge the effects of the economic downturn on giving, says Del Martin, chair of the Giving USA Foundation, although early figures show that donations rose in 2007. In general, people tend to give to causes closer to home. In 2006, Americans gave more than $295 billion to charity, but less than 4 percent of that went overseas.