The plan calls for establishing a permanent presence on the moon within two decades and to put astronauts on Mars sometime after 2030, the official said.
Congressional negotiators have previously agreed to a budget for the National Aeronautics and Space Administration of nearly $15.5 billion for fiscal 2004, which 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 by the Senate.
A 5 percent boost, as proposed by Bush, would increase the budget by an additional $775 million.
The official said part of the funding for the moon-Mars initiative would come from reallocation of money already in the budget of the National Aeronautics and Space Administration.
In a speech planned for Wednesday, Bush will talk of establishing a moon base that would be used as stepping stone to deeper space exploration, to Mars and perhaps beyond.
Part of the funding for the ambitious projects would come from phasing out of the space shuttle 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.
Bush's plan, the official said, calls for sending exploring robots to the moon by 2008, landing humans there by 2020 and then launching a Mars expedition after 2030.
The official said the president's address gives broad outlines to the moon-Mars projects, leaving details to be worked out by experts.
In remarks Tuesday in Mexico, Bush said the speech would address "America's approach to space exploration."
"The spirit is going to be one of continued explorationation ... seeking new horizons and investing in a program that ... meets that objective," he said.
Experts said that an effort to return to the moon will require building new spacecraft that could operate in that environment, able to land astronauts on the surface and then return them to lunar orbit or to Earth. They said the eventual plan could include sending robot craft to the moon and later to Mars to cache supplies for use later by human explorers.
Some have suggested that such an ambitious program would require developing some form of nuclear power. This would be needed to energize the lunar colony and later to provide dependable electricity for any extended Mars expedition.
NASA already is working to develop an electric-ion rocket that could be used to speed the months-long trip to Mars.
Much of the equipment and techniques needed for a Mars adventure could first be test at a lunar base.
The moon, with its gravity just one-sixth of the Earth's, might also be used as a jumping off point for voyages beyond the Earth's orbit, such as to Mars or to asteroids.
Some experts have proposed that a colony on the moon could exploit mineral rescources that are thought to be on the lunar surface. It's known that lunar soils contain helium-3, a potential fuel. Some studies also have suggested the moon may have water which could be chemically split to obtain hydrogen and oxygen, a combination that can be used as a rocket propellant. The oxygen could be used for an atmosphere inside sealed shelters.
By Paul Recer