The United States is focusing on providing clean water and basic sanitation in South Asian areas hit by an earthquake and tsunamis (search), to try to prevent illness and more deaths among survivors.

"Our efforts are focused, with the rest of the international community, on water and sanitation, because that is the greatest risk to people's lives," said Andrew Natsios, chief of the U.S. Agency for International Development (search), which distributes foreign aid.

Natsios predicted the death toll eventually may exceed 100,000.

Water and sewage systems were inundated by the enormous surge of water that hit coastal areas of 12 countries on Sunday following an earthquake (search) deep in the Indian Ocean. Debris and corpses are also a health hazard.

"People are drinking sewage water," Natsios said at a State Department briefing. "That will substantially increase the risk of communicable disease and diarrheal disease, which could kill many people in epidemics, if they get out of control."

President Bush assembled a four-nation coalition to organize humanitarian relief, and promised that the United States would help bankroll long-term rebuilding.

"It's just beyond our comprehension to think about how many lives have been lost," Bush said after emerging from a holiday vacation at his Texas ranch to make his first comments on the disaster.

Marc Grossman, undersecretary of state, will lead a U.S. task force to coordinate the American response and urge other nations to assist in relief efforts. He participated in a 40-minute conference call Wednesday night with senior Japanese, Australian and Indian officials.

State Department spokesman Noel Clay said they agreed to try to avoid duplicating efforts, by each other and the United Nations, to help the victims.

U.S. embassy officials continued to hunt for 2,000 to 3,000 Americans who remain unaccounted for in the coastal regions hit by the tsunamis, and asked travelers to check in with families and U.S. diplomatic posts. At least 12 Americans were known dead from Sunday's quake and subsequent tsunamis that struck a dozen countries from Thailand to Somalia.

From airlifts of rice and water purifiers to the deployment of an entire Marine expeditionary force, the United States marshaled resources across the globe to augment its initial $35 million aid package and make sure the hardest hit locations got the short-term help they requested.

Bush said he phoned the leaders of stricken countries to solicit specific needs and assure them the initial aid package "is only the beginning of our help." He also laid the foundation for a long-term international recovery plan by forming the coalition with Japan, Australia and India and inviting other nations to join.

Both the president and officials in Washington touted the breadth of U.S. aid, ticking off figures they hoped would rebut comments by a U.N. official and others suggesting that the United States had been stingy or slow to react.

The president called the U.N. official's comments Monday "very misguided and ill informed." His State Department spokesman was more blunt: "We don't have anything to apologize for," Richard Boucher said.