In a speech prepared for delivery Wednesday, Mr. Bush is calling for a lunar base to be established within two decades and a manned landing on Mars sometime after 2030, an official said.
The proposal comes after 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.
Mr. 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.
CBS News White House Correspondent Mark Knoller reports experts believe the actual cost of the moon and Mars projects could be as much as $750 billion.
Even if Congress does not approve the president's plan, it gives Mr. Bush a chance to discuss a bold proposal during an election year.
Increased NASA funding could also mean more jobs in key states. Of NASA's 12 main sites, three are in California and two are in Virginia. Texas, Ohio, Maryland, Alabama and Mississippi also host NASA centers.
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.
Part of the moon-Mars initiative would be funded by the reallocation of 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.
A less ambitious project proposed by Mr. 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.
But NASA administrator Sean O'Keefe says the cost will be a small part of annual budgets.
"It's going to be a methodical kind of developmental effort and it's basically going to amount to, much like we see every year, the cost of a monthly cable television payment that any individual makes is what the taxpayer typically contributes to what is amounting to less than 1 percent of the federal budget for what we're engaged in here," O'Keefe told the CBS News Early Show.
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. The eventual plan could include sending robot craft to the moon and later to Mars to cache supplies for use later by human explorers.
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.
Mr. Bush's plan calls for a new spacecraft, modeled on the Apollo capsules, to replace the aging fleet of space shuttles, reports CBS News Correspondent Thalia Assuras.
The only human-rated spacecraft now in the nation's arsenal are three space shuttles, aging winged craft limited to Earth orbit. The shuttle fleet has been grounded since Columbia exploded over Texas on Feb. 1, killing seven astronauts. The first post-Columbia launch is expected in about a year.
NASA is committed to completing the International Space Station, an effort that will take a series of space shuttle missions.
In addition to the costs involved, the prospect of a mission to Mars carries vast technical challenges. One is figuring out how to keep humans healthy during very long stays in low gravity. Another is finding water and fuel for use on Mars.
The top challenge, in the wake of the Columbia disaster, will be protecting astronauts lives during a voyage lasting six months each way.
"Everything we're engaged in has a huge element of risk involved," O'Keefe told the Early Show.