To pay for the new effort -- which would require a new generation of spacecraft but use Europe's Ariane rockets and Russia's Soyuz capsules in the interim -- NASA's space shuttle fleet would be retired as soon as construction of the International Space Station is completed, senior administration sources told United Press International.

The visionary new space plan would be the most ambitious project entrusted to the National Aeronautics and Space Administration since the Apollo moon landings of three decades ago. It commits the United States to an aggressive and far-reaching mission that holds interplanetary space as the human race's new frontier.

Sources said Bush's impending announcement climaxes an unprecedented review of NASA and of America's civilian space goals -- manned and robotic. The review has been proceeding for nearly a year, involving closed-door meetings under the supervision of Vice President Dick Cheney, sources said. The administration examined a wide range of ideas, including new, reusable space shuttles and even exotic concepts such as space elevators.

To begin the initiative, the president will ask Congress for a down payment of $800 million for fiscal year 2005, most of which will go to develop new robotic space vehicles and begin work on advanced human exploration systems. Bush also plans to ask Congress to boost NASA's budget by 5 percent annually over at least the next five years, with all of the increase supporting space exploration. With the exception of the Departments of Defense and Homeland Security, no other agency is expected to receive a budget increase above inflation in FY 2005.

Along with retiring the shuttle fleet, the new plan calls for NASA to convert a planned follow-on spacecraft -- called the orbital space plane -- into versions of a new spaceship called the crew exploration vehicle. NASA would end substantial involvement in the space station project about the same time the moon landings would begin -- beginning in 2013, according to an administration timetable shown to UPI.

The first test flights of unmanned prototypes of the CEV could occur as soon as 2007. An orbital version would replace the shuttle to transport astronauts to and from the space station. However, sources said, the current timetable leaves a period several years when NASA would lack manned space capability -- hence the need to use Soyuz vehicles for flights to the station. Ariane rockets also might be used to launch lunar missions.

During the remainder of its participation in space station activities, NASA's research would be redirected to sustaining humans in space. Other research programs not involving humans would be terminated or curtailed.

The various models of the CEV would be 21st century versions of the 1960s Apollo spacecraft. When they become operational, they would be able to conduct various missions in Earth orbit, travel to and land on the moon, send astronauts to rendezvous with nearby asteroids, and eventually serve as part of a series of manned missions to Mars.

Under the current plan, sources said, the first lunar landings would carry only enough resources to test advanced equipment that would be employed on voyages beyond the moon. Because the early moon missions would use existing rockets, they could deliver only small equipment packages. So the initial, return-to-the-moon missions essentially would begin where the Apollo landings left off -- a few days at a time, growing gradually longer. The human landings could be both preceded and accompanied by robotic vehicles.

The first manned Mars expeditions would attempt to orbit the red planet in advance of landings -- much as Apollo 8 and 10 orbited the moon but did not land. The orbital flights would conduct photo reconnaissance of the Martian surface before sending landing craft, said sources familiar with the plan's details.

Along with new spacecraft, NASA would develop other equipment needed to allow humans to explore other worlds, including advanced spacesuits, roving vehicles and life support equipment.

As part of its new space package, sources said, the administration will convene an unusual presidential commission to review NASA's plans as they unfold. The group would consider such factors as the design of the spacecraft; the procedure for assembly, either in Earth orbit or lunar orbit; the individual elements the new craft should contain, such as capsules, supply modules, landing vehicles and propellant stages, and the duration and number of missions and size of crews.