Albert "Jack" Stanley, the former director of global services for Kellogg Brown & Root pleaded guilty Wednesday to having paid bribes to Nigerian government officials for more than a decade, including while the construction and engineering firm was owned by Halliburton.

Stanley, who was fired when the bribery allegations surfaced in 2004, has agreed to cooperate with prosecutors still investigating how many people were involved in the conspiracy. Vice President Dick Cheney was C.E.O. of Halliburton from 1995 to 2000; the company acquired Kellogg Brown & Root in 1998.

Halliburton, which is based in Houston, said late Wednesday that it "has not yet reviewed the plea agreement, so it would be premature to comment."

Stanley, 65, made his plea before U.S. District Judge Keith B. Ellison of Houston. Neither the plea agreement nor the Department of Justice press release mention Halliburton or Kellogg Brown & Root by name.

But a separate, parallel civil complaint and press release from the Securities and Exchange Commission do name the company.

In his plea agreement, Stanley has admitted to participating in a conspiracy to bribe Nigerian officials to win $6 billion in contracts to build a liquefied natural-gas plant on Bonny Island in the oil-rich Niger River Delta region of Nigeria.

Kellogg Brown & Root was part of a consortium of Western companies seeking to build the plant, according to court records. Stanley was K.B.R.'s senior representative on the consortium's steering committee.

In that role, Stanley and others met with high-ranking Nigerian government officials on at least four occasions to arrange the bribe payments, the S.E.C. says.

Stanley and the others funneled money to Nigerian officials by using sham contracts with two "agents," whom the consortium paid more than $180 million over several years. Some of that money—U.S. investigators described them only as "substantial payments"—was sent to corrupt Nigerian government officials.

For his role in the scheme, Stanley admitted that he received about $10.8 million in kickbacks, which were paid to a dummy company in Panama or to a numbered Swiss bank account. As part of his plea deal, Stanley has agreed to surrender that amount to prosecutors, though it is unclear how much he still controls.

Separately from the Nigerian investigation, critics have blasted K.B.R. for having received billions of dollars' worth of Pentagon contracts to feed, house, and supply U.S. troops in Iraq.

Many of those contracts were awarded without competitive bidding, and several have resulted in allegations of overcharging, poor management, and corruption. At one point, for example, K.B.R. billed the government more than $27.5 million to truck $82,100 worth of liquefied petroleum gas from Kuwait to neighboring Iraq.

The Defense Contract Audit Agency, which later dismissed that bill as "illogical," has repeatedly criticized K.B.R.'s billing system.

In some cases, K.B.R. employees took it upon themselves to steal supplies intended for U.S. troops or accept bribes to let others steal them.

At a Congressional hearing in July, a former Army contracting officer said that the Pentagon's oversight of K.B.R.'s work in Iraq and Afghanistan was "irregular and highly out of the ordinary."