Darleen A. Druyun, 56, of Vienna, Va., entered the plea in U.S. District Court to a single count of conspiracy, which carries a maximum five years in prison.

"I deeply regret my actions and I want to apologize," she said, her voice breaking slightly. She will be sentenced on Aug. 6, and faces a fine of up to $250,000 and five years in prison.

Druyun was an Air Force procurement officer before becoming a vice president at Boeing. She and former Boeing chief financial officer Michael Sears were the subject of a federal grand jury investigation of the Air Force's plan to acquire 100 refueling tankers from the Chicago-based jet maker.

Boeing fired Druyun and Sears in November for what the company termed unethical behavior.

Boeing officials said Sears improperly contacted Druyun about a possible top-level company job in 2002, when she still was at the Air Force and playing a key role in deciding whether Boeing should get the tanker contract, which could be worth up to $23 billion.

Druyun retired from the Air Force in November 2002 and joined Boeing in January 2003 as deputy general manager of its Missile Defense Systems unit.

U.S. Attorney Paul McNulty said that the case "points out how important conflicts of interest are" and said he hoped the plea sent a message to other government officials in charge of contracts.

"There can be only one interest, the public's," McNulty said. He said Druyun has agreed to cooperate in what he called an ongoing investigation.

The tanker contract, eventually awarded to Boeing, is under suspension while a series of reviews are conducted.

The Air Force wants to acquire 100 modified Boeing 767 aircraft to modernize its aging fleet of aerial refueling tankers. The Pentagon's inspector general has said the unusual lease-purchase arrangement is more expensive than buying the planes outright, and said significant changes should be made before the deal is allowed to proceed.

In a highly critical report this month, Inspector General Joseph Schmitz said procedural and financial problems with the deal could cause the government to spend as much as $4.5 billion more than necessary.

Sen. John McCain, R-Ariz., the deal's sharpest critic, has called it corporate welfare for Boeing, which has cut nearly 40,000 jobs since the 2001 terrorist attacks sent the aviation industry into a tailspin. McCain has said Druyun's actions demonstrate the "incestuous relationship between the defense industry and defense officials that is not good for America."

Boeing officials have said they expect the deal to go forward but are prepared to take a $310 million charge if it collapses. In a statement Tuesday, the company noted that it had cooperated with the U.S. attorney's office and others investigating the case.

"It is important to note the charge announced today relates to conflict-of-interest in Ms. Druyun's hiring and is not related to Boeing business, its financial performance or the 767 Tanker program," the company said in the statement. "Today's events represent another step toward concluding a very disappointing chapter in the company's 88-year history of serving our customers and operating with the highest integrity."

As part of the agreement, the government agreed not to prosecute Druyun's daughter, Heather, who works at Boeing and was involved in e-mail negotiations with Sears.