Bethesda-based contracting giant Lockheed Martin said incoming chief executive Christopher E. Kubasik has resigned because of a “close personal relationship with a subordinate employee” and Marillyn A. Hewson, who was in line to become president and chief operating officer, will become chief executive.

Kubasik, Lockheed’s chief operating officer and president, was expected to take over leadership of the company from Robert J. Stevens on Jan. 1.

The company said Friday that it asked for his resignation after “an ethics investigation confirmed that he had a close personal relationship with a subordinate employee.”

“His actions violated the company’s Code of Ethics and Business Conduct, but did not affect the company’s operational or financial performance,” Lockheed said in a press release.

Kubasik was promoted last year to serve with Stevens in a two-person executive office that the company said would allow it to be more responsive to its government customers. He has been president and COO since January 2010 and has previously led Lockheed’s electronic systems business and served as chief financial officer.

Hewson will take over on Jan. 1, according to Lockheed. She has led the contractor’s electronic systems unit since January 2010 and has been with Lockheed for 29 years.