It is unclear where the program, known as Artemis, will head after President-elect Donald J. Trump returns to the White House in January.
NASA on Thursday postponed a mission to send four astronauts around the moon and back to Earth until April 2026.
The move is the latest setback for Artemis, the government space agency’s return-to-the-moon program, which has already faced years of delays.
A subsequent mission to land astronauts near the south pole of the moon is now scheduled for mid-2027, Bill Nelson, the NASA administrator, said during a news conference on Thursday.
The adjustment to the Artemis schedule comes as the Mr. Nelson prepares to leave the agency when President-elect Donald J. Trump returns to the White House in January.
Even though Mr. Trump had set the goal of sending astronauts back to the moon during his first administration, he could change his mind after he takes office. In the coming months, NASA could instead put more money toward another destination that Mr. Trump has talked about: Mars.
The first of the two missions that were delayed on Thursday, known as Artemis II, is set to be the first in more than 50 years to send astronauts close to the moon. It will also be first time that astronauts launch on top of NASA’s giant new Space Launch System rocket and then swing around the moon inside a crew capsule called Orion before returning to Earth and splashing down in the Pacific Ocean. The mission will not land on the moon.