President Bush wants to set NASA (search) on a new course for exploring the far reaches of the solar system, starting with a long-term research base on the moon — but the White House says the venture won't require major spending increases in the short run.

Bush, who was laying out his vision in a speech Wednesday at the space agency's headquarters, will offer "a new plan to explore space and extend a human presence across our solar system," said White House spokesman Scott McClellan. He said the proposal "will give NASA a new focus and long-term vision for future exploration that will focus on a renewed spirit of discovery."

Bush is asking for a $1 billion boost to NASA's budget over five years to fund the start of a new American campaign in space intended to put a the base on the moon and to land astronauts on Mars, administration officials say. Bush is calling for a lunar base to be established within two decades and a manned landing on Mars (search) sometime after 2030, an official said.

Part of the moon-Mars initiative would be funded by shifting money already in NASA's budget, officials said. The plan calls for retiring the space shuttle by the end of this decade and quickly concluding the U.S. obligations to the International Space Station. The shuttle now costs NASA about $4 billion a year and the station about $1 billion.

Sensitive to questions about whether the nation can afford a new space venture at a time of record federal deficits, McClellan said NASA spending, in the short term, would constitute less than 1 percent of the federal budget.

"We're spending less than 1 percent of the federal budget on the science and technology that NASA employs for exploration objectives," NASA administrator Sean O'Keefe (search) said Wednesday on NBC"s "Today" show, "and that won't change. It's about exploration. It's about how do you redirect the focus of what we do toward those broad objectives that the president will outline."

Members of Congress and others have called for a new national vision for the National Aeronautics and Space Administration, urging a human space initiative that would reinvigorate an agency wounded by last year's loss of space shuttle Columbia and trapped by expensive projects that limit manned spaceflight to low Earth orbit.

Bush, speaking with reporters Tuesday on a trip to Mexico, said his plan centers on human exploration of space.

"The spirit is going to be one of continued exploration ... seeking new horizons and investing in a program that ... meets that objective," he said.

His proposal for $1 billion over five years, in effect, would provide startup funds for highly complex projects that could take decades and may require hundreds of billions of additional dollars to complete.

Congressional negotiators last year agreed to a NASA budget of nearly $15.5 billion for fiscal 2004, the budget year that began last Oct. 1. That's a $90 million boost over the previous year. The measure, part of a broad-based spending bill, was passed by the House and awaits approval in the Senate.

A less ambitious project proposed by Bush's father called for putting astronauts on Mars, but did not mention a moon base. The cost of that project in 1989 was projected at $400 billion to $500 billion, a price tag that discouraged Congress. The project was never started.

Experts say that under the latest plan, robots would be sent to the moon by 2008 and astronauts ready to build a lunar base would land there by 2020. The plan envisions using the moon as a staging area for deeper space exploration with a landing on Mars after 2030.

An official said the president's address will give broad outlines to the moon-Mars plan, leaving details to be worked out later. The administration's officials spoke on condition of anonymity.

Experts said the effort to return to the moon would require building new spacecraft, and the eventual plan could include sending robot craft to the moon and later to Mars to cache supplies for use later by human explorers.

A colony on the moon, experts say, could be used to exploit mineral resources of the lunar surface, such as helium-3, an isotope that theoretically could be used for rocket fuel. There are suggestions that the moon has deposits of water near its poles. Water could be chemically split to obtain hydrogen and oxygen, a combination that could be used as a rocket propellant. The oxygen could be used for an atmosphere inside sealed shelters.