NASA is considering extending the timeline to start establishing a base for humans on the moon, potentially disrupting a central element of President Trump’s space ambitions.

Trump administration officials have long said plans to return U.S. astronauts to the lunar surface also had to simultaneously lay the groundwork for setting up living and working facilities there. Vice President Mike Pence has repeatedly stressed that such a longer-term human presence was essential for developing technologies to explore deeper into the solar system.

National Aeronautics and Space Administration budgets and policies were built around the concept of using an orbital staging platform, called a lunar gateway, to assemble crews, vehicles and materials for missions to begin construction of bases on the moon. Such missions, possibly shipping stockpiles of water, food and building materials, were supposed to start no later than 2025.

But on Saturday Doug Loverro, NASA’s top human-exploration official, signaled that schedule could slip at least a year as NASA reconfigures the design and use of that gateway. “We are looking at alternatives,” he said in an interview, “to make sure we can achieve sustainability as soon as possible.”

Mr. Loverro also said significant changes to the gateway are intended to reduce overall cost and risk.