HOUSTON — An operation that pumped heavy drilling mud to plug BP’s runaway oil well in the Gulf of Mexico has been so successful that Obama administration officials said on Wednesday they were convinced the well would never leak again.

BP began the effort, known as a static kill, late Tuesday and then stopped pumping the mud after eight hours to verify that it had not caused the Macondo well to spring any new leaks.

Throughout the day, senior government scientists and BP engineers combed through data to evaluate the condition of the well piping and whether it made sense to pour cement for a final plug from a surface ship above the well or to pump the cement through a relief well that is still being drilled.

BP and government officials said late Wednesday that they would proceed on Thursday with a permanent cementing of the well, and that there was no doubt that the static kill represented a major step in bringing the well under control.