American astronauts will return to the moon early in the next decade in preparation for sending crews to explore Mars and nearby asteroids, President Bush is expected to propose next week as part of a sweeping reform of the U.S. space program. 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.