Florida ? For the second time in less than a week, a potentially dangerous hydrogen gas leak early Wednesday forced NASA to delay shuttle Endeavour’s launch to the international space station, this time until July at the earliest.

Launch officials waited almost an hour after the leak appeared during fueling, trying to fix it through remote commands, before calling off the predawn launch.

The leak occurred in the same place as one that cropped up Saturday, in the hydrogen gas vent line that hooks up to the external fuel tank. A similar problem stalled a shuttle flight three months ago.