Chicago ? Boeing Co. chairman and CEO Phil Condit resigned unexpectedly Monday amid deepening turmoil over questionable tactics used by the aerospace giant in aggressively trying to win defense contracts.

The stunning resignation came a week after two executives were fired for unethical conduct, including chief financial officer Mike Sears, who had worked closely with Condit at Boeing’s Chicago headquarters.

Condit, 62, said he quit to try to prevent the company from getting “bogged down” after a year of tumult involving its defense business.

“I ultimately concluded it was the best decision for the good of the company,” he said. “The controversies and distractions of the past year were obscuring the great accomplishments and performance of this company.”

Among other things, the Pentagon is investigating allegations that a former Air Force official gave Boeing information about another company’s competing bid on a contract to supply the military with air-refueling tankers.

The Air Force official, Darleen Druyun, was later hired by Boeing as a vice president, and Boeing eventually won the estimated $17 billion contract. Last week, Druyun was fired along with Sears, who had talked to her about a job with Boeing while she was still at the Pentagon.

Boeing — one of Kansas’ top private employers — has had other troubles with the Defense Department in recent months.

In July, the Pentagon punished the company for stealing trade secrets from rival Lockheed Martin to help win rocket contracts. Boeing has been barred from bidding on military satellite-launching contracts, a penalty that has cost it seven launches worth about $1 billion.

Condit has not been connected to the ethical issues that resulted in the recent firings.

The scandal has done serious damage to the image of a storied company whose roots date to the invention of the airplane a century ago. Founded by William Boeing, the company had a huge effect on the development of commercial aviation in the 1900s.

Boeing employs about 160,000 people — including more than 12,000 in Wichita, Kan. — and has churned out thousands of jets and rockets that have been used by airlines, the military and space program.

Condit had been with Boeing since 1965, when he joined the company as an aerodynamics engineer. He became CEO in 1996 and was named chairman in 1997.

Condit moved company headquarters to Chicago from Seattle in 2001 and reduced the company’s historical reliance on commercial jets, beefing up its defense and space operations in a strategy that helped cushion the severe blow to the aviation business after Sept. 11.

But he has also been criticized for leading Boeing away from the jetliner business. Rival Airbus is expected to eclipse Boeing this year as the world’s largest commercial jet manufacturer.

Boeing rushed to install new leaders Monday.

The company brought back Harry Stonecipher, its 67-year-old former president and chief operating officer, from retirement in Florida to become chief executive in what analysts saw as caretaker leadership.

It also split Condit’s duties in two, naming board member and former Hewlett-Packard Co. CEO Lewis Platt as chairman.

Even Boeing backers in Washington were hesitant to say the company’s troubles involving the tanker deal are over.

“I hope this is the end of it,” said Rep. Norm Dicks, D-Wash., a leading proponent of the tanker deal. “But I don’t know. There are still other investigations by the IG (inspector general) and internally by Boeing that are under way.”

Pentagon officials said the resignation was a private company matter and declined to comment on the inspector general’s investigation.

Despite Condit’s solid reputation, the company’s stock held steady on news of his departure. Boeing was down just 37 cents to $38.02 on the New York Stock Exchange.