And the United States has a lot of work to do to help Indian Ocean countries build an early warning system similar to one that protects Japan and the US West Coast, they said.

The giant quake of magnitude 9 off the coast of the Indonesian island of Sumatra lifted the sea floor 15 feet (4.5 metres) and displaced trillions of gallons of water, causing the monster wave that inundated coastlines thousands of miles away, said Dr. Charles Groat, director of the US Geological Survey.

"The run-for-your-life business has to be communicated very quickly and very effectively and that's a challenge even in our country," Groat told a hearing of the Senate Committee on Science, Commerce and Transportation.

"In the countries we are talking about it is a whole other order of magnitude to do these."

Groat said there was "unevenness" in progress toward a tsunami early warning system in the region.

"The most capable countries, well on their way to building systems like ours, are countries like India, Australia, Indonesia and Thailand," Groat said.

"The United States will participate ... in advising and helping those nations to develop strong programs."

But the United States also has to finish its own network of early monitoring and warning system for quakes and tsunamis, the experts said.

Groat said USGS was moving to a 24-hour-a-day system and was upgrading software and other programs.

John Kelly, Deputy Undersecretary at the National Oceanic and Atmospheric Administration, said his agency had to expand its work, also.

"Over the past eight years we have identified what needs to be done, but so far there are inundation maps for only 30 percent of the Pacific states coastline, local communities are in need of warning dissemination systems, and the NOAA tsunami warning system needs more deep ocean tsunami detectors to improve warning services," Kelly said.

This includes three of six buoys designed to detect tsunamis as they travel, virtually invisible, across the deep sea. Such waves do not usually raise water levels much until they hit a shallow shoreline.

Three Deep-ocean Assessment and Reporting of Tsunamis, or DART buoys, off Alaska's Aleutian Islands and the coast of Washington are broken and the weather is too foul to get a boat out to repair them, Kelly said.

Two others off the West Coast and one in the eastern Pacific are working. "While the three are down, and that's regrettable ... we are not totally defenseless," Kelly said.

White House Science Adviser John Marburger said the needed technology was all available.

"The agencies indicated to us that they ought to have substantial improvement of the system within two years," he said.

With 85 percent of tsunamis occurring in the Pacific, the threat to the United States is clear, the experts said. There are also active volcanoes and fault zones in the Caribbean than can generate tsunamis.