By Irene Klotz

CAPE CANAVERAL, Florida (Reuters) - NASA said on Monday it plans to build a permanently occupied base on the moon, most likely at the lunar south pole.

The habitat will serve as a science outpost as well as a testbed for technologies needed for future travel to Mars, and construction will follow a series of flights to the moon scheduled to begin by 2020.

"We're going for a base on the moon," Scott "Doc" Horowitz, NASA's associate administrator for exploration, told reporters in a teleconference from the Johnson Space Center in Houston.

Plans for what the base will look like and what astronauts would do there have yet to be determined. Similarly, NASA has not projected a date when the base would go into operation.

The moon's polar sites are preferred to equatorial regions because of more moderate temperatures and longer periods of sunlight, which is critical for the solar-powered electrical systems NASA plans to develop. Eventually, nuclear power may be used to augment or replace the solar energy systems.

Scientists also suspect the poles have resources such as hydrogen, ice and other materials that could be used for life support.

"It's exciting," said NASA deputy administrator Shana Dale. "We don't know as much about the polar regions."

The United States had already announced plans to develop new spacecraft to travel to the moon and land on its surface for the first time since the last Apollo flight there in 1972. It also plans to provide a communications system linking Earth and the moon.

But NASA doesn't plan to go to the moon alone. The United States will look for international and commercial partners to share the expense and possibly provide components such as additional power systems, living quarters and resources for surface travel on the moon.

NASA is not expecting a budget increase to pay for the program. Rather, it will transition funds currently being used to support the space shuttle into the moon exploration program as the shuttle fleet is phased out.

The shuttles are set to be retired in 2010. By that time, NASA plans to have finished building the space station, leaving the moon initiative as a successor to both programs. NASA receives about $16 billion a year.

Countries and agencies that already have been working with NASA to develop its so-called Global Exploration Strategy are Australia, Canada, China, France, Germany, the United Kingdom, India, Italy, Japan, Russia, South Korea, Ukraine and the European Space Agency.

Copyright © 2006 Reuters Limited.