JOHN F. KENNEDY SPACE CENTER, Fla.—NASA is likely to remove its massive moon rocket from a launchpad after scrubbing a second attempted launch Saturday, a move that could delay the planned Artemis I mission by several weeks, officials said.

 Rolling the agency’s Space Launch System rocket back to a facility here, NASA officials said, would allow engineers to work on resolving a hydrogen leak that prompted engineers to again delay the Artemis I launch, intended as the first step in the agency’s multiyear plan to land astronauts on the moon. NASA leaders also discussed potentially conducting that work on the launchpad, leaving the rocket in place.

NASA Administrator Bill Nelson said the decision to postpone Saturday’s planned launch, which came after the agency earlier in the week called off its first try, was prudent. Three attempts to stop what officials described as a large hydrogen leak failed, pushing launch teams to ultimately set aside plans for a blastoff earlier in the afternoon. 

“We don’t have the launch that we wanted today,” Mr. Nelson said at an afternoon briefing Saturday. He said that safety is the agency’s priority, and NASA won’t try to blast off the rocket until it is ready. 

NASA won’t attempt a launch on Monday, Sept. 5, or Tuesday, Sept. 6, other potential windows that the agency had previously identified if Saturday’s launch didn’t proceed. A launch period including those dates is “definitely off the table,” said Jim Free, the agency’s associate administrator focused on developing exploration systems.

Determining if another attempt is possible later in the fall, including October, will depend on the options NASA’s teams deliver, likely early next week, Mr. Free said. 

The hydrogen leak emerged during the fueling process Saturday and couldn’t be contained despite multiple attempts to fix it, the agency said. The leak related to a “quick disconnect” connection on a line used to flow liquid-hydrogen into a huge tank on the Space Launch System, the towering rocket that the National Aeronautics and Space Administration wants to use to start its Artemis missions, which aim to return astronauts to the surface of the moon. 

The SLS rocket uses super-cold liquid hydrogen and liquid oxygen as propellants, and filling its enormous tanks with them is a challenge. Hydrogen is a very small molecule and can escape efforts to contain it, NASA officials have said.

The agency said after a practice run in June that it would take fresh steps to deal with a hydrogen leak, and NASA was able to manage through a leak during fueling on Monday, before that launch was called off because of problems with an engine-cooling procedure.