President Obama will seek to promote his vision for the nation’s human space flight program on Thursday, just two days after three storied Apollo astronauts — including Neil Armstrong, the first human to walk on the Moon — called the new plans “devastating.”

In an announcement to be made at the Kennedy Space Center in Florida, the president will personally talk for the first time about the sweeping upheaval of the National Aeronautics and Space Administration’s human spaceflight program outlined in his 2011 budget request: canceling the current program that is to send astronauts back to the Moon, investing in commercial companies to provide transportation to orbit and developing new space technologies.

A senior administration official said Mr. Obama would describe a vision “that unlocks our ambitions and expands our frontiers in space, ultimately meaning the challenge of sending humans to Mars.” The official spoke with administration approval, but on the condition of anonymity so that the comments would not upstage the president’s remarks.

Mr. Obama’s budget request called for the cancellation of Orion crew capsule, which was to be used to carry astronauts to the International Space Station and then to the Moon, as well as other components of the current program known as Constellation.