The latest procedure to try to contain the oil gushing into the Gulf of Mexico hit a snag on Wednesday when a saw that was being used in a crucial part of the operation became stuck, officials said.

The diamond-laced wire saw was being used to cut the riser, the milelong pipe that once ran from the wellhead up to the drilling rig and now snakes along the seabed. A technician involved in the effort said that the wire saw had cut less than halfway through the riser when it stopped being effective. The saw was freed later Wednesday afternoon.

The technician, who spoke on condition of anonymity because he was not authorized to comment on the work, said it appeared that the saw was dulled by material inside the riser - including, perhaps, some of the objects pumped into the well during the failed "top kill" procedure last week.

The cut was part of a strategy to place a containment cap over the well and funnel the leaking oil up through a new riser to a ship on the surface. A variation on this tactic was tried several weeks ago with a 98-ton box that was to sit over the worst of the leaks, but it failed when the box became clogged with hydrates, icelike crystals of gas and water.