WASHINGTON – Early finger-pointing erupted Monday among companies involved in the oil rig explosion in the Gulf of Mexico and unstopped leak of millions of gallons of oil, on the eve of the first congressional hearings into the accident.

A top American executive for BP, Lamar McKay, said a critical safety device known as a blowout preventer failed catastrophically. Separately, the owner of the rig off Louisiana’s coast said BP managed it and was responsible for all work conducted at the site. A third company defended work that it performed on the deep-water oil well as “accepted industry practice” before last month’s explosion.

“We are looking at why the blowout preventer did not work because that was to be the fail-safe in case of an accident,” McKay, chairman and president of BP America, said in testimony prepared for a Senate hearing today. A copy of his testimony was obtained by The Associated Press. “Transocean’s blowout preventer failed to operate.”

The chief executive for Swiss-based Transocean, which owned the oil rig and the blowout preventer, shifted blame to BP.

“All offshore oil and gas production projects begin and end with the operator, in this case BP,” CEO Steven Newman said in his Senate testimony, also obtained by the AP. Newman said BP was responsible for submitting a detailed plan specifying where and how a well is to be drilled, cased, cemented and completed.

Newman also said BP’s contractor, Halliburton Inc., was responsible for encasing the well in cement, putting a temporary plug in the top of the well and ensuring the cement’s integrity. That cementing process was dictated by BP’s well plan, Newman said.

A Halliburton executive, Tim Probert, said the company safely finished a cementing operation 20 hours before the rig went up in flames. Probert said Halliburton completed work on the well according to accepted industry practice and at the direction of federal regulators.

The blame game took hold on Capitol Hill as Congress and federal investigators were to begin a series of hearings in Washington and on the Gulf Coast. Two Senate hearings were set for today, and a House hearing was scheduled for Wednesday. In Louisiana, near the disaster site, a six-member panel that includes investigators from the Interior Department and Coast Guard was to begin two days of hearings.

McKay, the BP executive, said the company has at least 40 people internally investigating the accident, but he acknowledged that the cause is still a mystery. Transocean has its own investigative team, Newman said.

“We are looking at our own actions and those of our contractors,” McKay wrote in his Senate testimony.