HOUSTON — An official for Halliburton, the company hired by BP to perform a critical step in the process for closing the well connected to the Deepwater Horizon oil rig, testified Tuesday that days before the rig exploded he had raised concerns to BP about its plan for executing the procedure, but that he continued with the job anyway.

The official, Jesse Gagliano, a shore-based technical adviser, told federal investigators here that he had recommended BP use a greater number of devices called “centralizers” in the well for the tricky step known as cementing, which is a method of sealing a well to control pressure from the oil and gas beneath. He said he was ignored.

Centralizers help cement flow evenly around an oil well before hardening, and using six of them — instead of the 21 that he recommended — made the well more likely to need additional cementing, Gagliano said.

Investigators say they believe the cement poured by Halliburton may have failed under tremendous pressure on April 20, producing the oil rig explosion that led to the largest deep-water oil spill in U.S. history.

Responsibility

Gagliano and Rick Godfrey, a BP lawyer, disputed whether Halliburton or BP should be responsible for the final cement plan.

The testimony, before an eight-member panel of federal government investigators, provided a fuller portrait of workers’ potentially risky decisions in the days before the disaster: not conducting a test called a “cement bond log,” not using a potentially safer type of well casing, and not conducting a “bottoms-up” test of the drilling solution in the well.

In a report to BP two days before the disaster, Gagliano noted that a reduced number of centralizers could cause a “severe gas flow” problem. By the morning of the disaster, BP had more centralizers flown to the rig, but decided not to install them, Gagliano said.

But internal Halliburton documents suggest that company employees believed that the cement job had been conducted properly by the day of the disaster.