NEW ORLEANS — A pivotal moment in the Gulf oil crisis hit an unexpected snag Tuesday evening when officials announced they needed more time before they could begin choking off the geyser of crude at the bottom of the sea.

BP and government officials did not say what prompted the decision or when the testing on the new, tighter-fitting cap would begin. The oil giant was scheduled to start slowly shutting off valves on the 75-ton metal stack of pipes and valves Tuesday, aiming to stop the flow of oil for the first time in three months.

A series of methodical, preliminary steps were completed, including mapping the seafloor. Later Tuesday, National Incident Commander Thad Allen met with the federal energy secretary and the head of the U.S. geological survey and other scientists and geologists.
“As a result of these discussions, we decided that the process may benefit from additional analysis that will be performed tonight and tomorrow,” Allen said.

Earlier Tuesday, it seemed BP was on track to test the cap, which was lowered over the blown-out well Monday night. It is designed to be a temporary fix until the well is plugged underground.